April 2020–March 2021

Kavli IPMUANNUAL REPORT 2020

CONTENTS
FOREWORD

2

1 INTRODUCTION

4

2 NEWS & EVENTS

14

3 ORGANIZATION

16

4 STAFF20

5 RESEARCH HIGHLIGHTS

26

5.1 Gopakumar-Vafa Type Invariants on Calabi-Yau 4-Folds ���������������������������������������������������������������������������������������������������� 26
5.2 (Co-) Evolution of Supermassive Black Holes and Their Host Galaxies�������������������������������������������������������������������������� 28
5.3 XENONnT – Finding Dark Matter Particles with Liquid Xenon ������������������������������������������������������������������������������������������ 30
5.4 Guided by EGADS, Loading Super-Kamiokande with Gadolinium for the First Time ������������������������������������������ 32
5.5 Subaru Prime Focus Spectrograph (PFS): Towards Science Operation ������������������������������������������������������������������������ 34
5.6 Resolution of Singularities of Thermal Correlators in String Theory ������������������������������������������������������������������������������ 37
5.7 Perverse Sheaves and Their Categorification �������������������������������������������������������������������������������������������������������������������������� 38
5.8 Milky Way Dark Matter Severely Constrained by Two New Papers �������������������������������������������������������������������������������� 39
5.9 Foreground Effect on the J-Factor Estimation of Dwarf Spheroidal Galaxies ���������������������������������������������������������� 40
5.10 Sign of Hard X-Ray Pulsation from the Gamma-Ray Binary System LS 5039 �������������������������������������������������������������� 42
5.11 Identifying the Origin of Black Holes �������������������������������������������������������������������������������������������������������������������������������������������� 44
5.12 Diversities of Supernovae and Their Origin ������������������������������������������������������������������������������������������������������������������������������ 45

6. AWARDS

48

7. CONFERENCES

50

8. CONFERENCE PRESENTATIONS AND SEMINAR TALKS

51

9. OUTREACH AND PUBLIC RELATIONS

52

Copyright © 2020 Kavli IPMU
All rights reserved
Editors: Tomiyoshi Haruyama (Chair), Chiaki Hikage, Misao Sasaki, Junichi Kanzaki
Editing Staff: Shoko Ichikawa
Kavli Institute for the Physics and Mathematics of the Universe
UTIAS, The University of Tokyo
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan
Tel: +81-4-7136-4940 Fax: +81-4-7136-4941
https://www.ipmu.jp/
April 2020–March 2021

Kavli IPMUANNUAL REPORT 2020

On the cover:Looking directly down into the Super-Kamiokande detector after it was drained in
preparation for loading with gadolinium. Inset: Kavli IPMU Professor and PI Mark Vagins
holds a bag of gadolinium sulfate octahydrate in the EGADS laboratory of the Kamioka
Observatory (Credits: Mark Vagins, Kai Martens).

Foreword

Foreword

This Annual Report covers the period from April 2020 to March 2021. Our Long-Term Strategic Planning
Report in 2019 identifies astrophysics surveys, cosmic microwave background (CMB) experiments, andKamioka underground experiments as our three priority areas. I am pleased that our projects in these areas
are making significant progress even during the pandemic, as you will see in Section 5 of this Annual Report.
The Planning Report also recommended two new initiatives. One is the applications of X-ray and gamma-ray
imaging techniques developed in astrophysics to medicine, in particular imaging of cancer stem cells in vivo.
This project is in collaboration with the JAXA Institute of Space and Astronautical Science, the National Cancer
Center, and the Institute for Advanced Medical Research at Keio University. Another is to develop new concepts in table-top experiments to explore the dark sector of the universe. Our scientists in this area collaborate
with the optical lattice clock project led by Hidetoshi Katori in the Department of Applied Physics of the University of Tokyo. The 2019 Long-Term Strategic Planning Report will guide us in the coming years, when we
make a transition from an institute with a fixed-term funding from the WPI program to a permanent institutewith stable funding.
Talking about our transition to a permanent institute, we heard wonderful news in March 2021 that the University of Tokyo approved our proposal to place the university funding for the Kavli IPMU in the “core expenses” category, at about one billion yen per year. Being part of the core expenses category means that thisfunding is secure and permanent. Together with the income from the Kavli IPMU endowment established in2012 and more than doubled in 2020, and with other fruits of our fundraising from both private and government sources, we will be able to operate at our current high level of research, perpetually. Section 5 of thisAnnual Report describes a variety of research projects conducted at the Kavli IPMU.

Hirosi Ooguri
Director

In my inaugural address as the Director of the Kavli IPMU in October 2018, I stated my commitment to provide
an inclusive and supportive environment to the diverse group of people in our community. Following up on
this promise, we are launching the Kavli IPMU Diversity Initiative in the 2021 – 2022 academic year. I plan towrite about these in the next year’s Annual Report.
I hope you will enjoy this report.

Though the COVID-19 pandemic continues to pose challenges to all of us, as I write this preface, we are
beginning to see the light at the end of the tunnel thanks in part by the rapid rollout of the mRNA
vaccine. As Anthony Fauci, the Chief Medical Advisor to the President of the United States, so eloquently wrote in his editorial article published in Science entitled “The story behind COVID-19 vaccines” [1],the success of the mRNA vaccine powerfully demonstrates the importance of long-term investments in basic
science research. Here is what he wrote at the end of the article: “The speed and efficiency with which thesehighly efficacious vaccines were developed and their potential for saving millions of lives are due to an
extraordinary multidisciplinary effort involving basic, preclinical, and clinical science that had been underway—out of the spotlight—for decades before the unfolding of the COVID-19 pandemic. When the stories
and recounting of this pandemic are written, it is important that this history not be forgotten, as we arereminded once again of the societal value of a sustained and robust support of our scientific enterprise.”Though we cannot foresee which basic research will benefit the humanity decades from now, the history tells
us that supporting a broad range of research driven by the curiosity of researchers is the best investment
strategy.

2

Kavli IPMU Annual Report 2020

Hirosi Ooguri

Reference:[1] A. S. Fauci, Science 372, 6538 (2021) 109

Kavli IPMU Annual Report 20203

1

Introduction

F

Y2020 is the fourth year from the five-year extension period of the WPI funding. We have proposed the following nine challenges for theextension period addressing new objectives. Below aresummaries of our effort to meet each challenge.
1. Creating new areas and tools of statistics, integrating mathematics with observation and experiments
A team led by N. Yoshida has developed machinelearning-based data analysis tools for Subaru Hyper
Suprime-Cam Sky Survey (HSC Survey hereafter) andthe Tomo-e Gozen project. They use the big astronomical data from HSC Survey to (1) detect and classify transient objects such as supernovae, and (2) reconstruct
the large-scale matter distribution in the universe. For
their objective (1), they have developed a multi-label
classifier that automatically identifies and classifies
astronomical transients into multiple types including
the most important Type Ia supernovae. They have also
tested several methods to detect transients from multipetabyte movie data to be delivered by Tomo-e Gozen.
For their objective (2), they have proposed a sparsitybased model to reconstruct a three-dimensional density field from HSC weak lensing data. Both the methods have been successfully applied to HSC data. In
particular, their transient classifier achieved 95.3%
accuracy for the three-class supernova classification.
2. Creating new synergies among fields not imaginedat the launch
The team led by T. Takahashi has been organizing interdisciplinary activities to develop advanced detectors
which could meet the needs in the field of nuclear
medicine. They have established a network withresearchers from the National Cancer Center, theDepartment of Medicine at Keio University, the Department of Medicine at Osaka University, RIKEN, and theCentre for Advanced Imaging at The University of
Queensland. Under this network, they have started
various bio-medical imaging experiments by using theimaging system developed at the Kavli IPMU. In 2020,

4

Kavli IPMU Annual Report 2020

Introduction

INTRODUCTION
they have performed various kinds of in vivo imaging
211
experiments using a short-lived radionuclide, At,with phantoms and tumor-bearing mice. The aim wasto establish a detector that can use for the evaluation ofin vivo biodistribution and dosimetry of therapeutics
containing alpha particle emitting radionuclides. To
study their pharmacokinetics of low concentrations,
two systems, one is based on the multi-pinhole imaging system and the other is based on a parallel collimator, were used. Both detectors have a high energy resolution of ΔE=1-2 keV (FWHM), which is required toresolve multiple characteristic X-rays emitted from thedecay of the radionuclide. They have succeeded todemonstrate the performance to isolate and identify all
signals from multiple radionuclides, including the scattering component in the target.
3. Discovering new major frameworks for geometric
thinking in mathematics and physics with the derived
and noncommutative geometry, such as to unify
various types of dualities
Noncommutative and derived geometry are powerfultools that allow us to enrich various familiar spaces ingeometry to more sophisticated objects for which thefunctions may not commute, property motivated byquantum mechanics, or be equipped with a cohomological differential structure analogous to a supercharge in physics. Such enrichments can be defined ina purely mathematical fashion and turned out to bevery useful in applications both to pure mathematics
and to mathematical physics. Further, the study ofderived categories of coherent sheaves combines bothnoncommutative and cohomological methods. In thederived geometry direction, Y. Toda introduced a newconcept of d-critical (i.e., derived critical) loci. This
allowed him to extend several fundamental results ofbirational geometry (such as wall-crossing equivalences) to a broad class of derived moduli spaces importantin physics. One of the tools to study wall-crossing has
been the cohomological Hall algebra (COHA) but its
precise definition was restricted to quiver-like situa-

tions. M. Kapranov and E. Vasserot provided a definition
and a study of COHA for algebraic surfaces, based on
ideas of derived geometry. A little later, F. Sala and M.
Porta gave a direct definition of the K-theoretical version, using derived moduli spaces. This work has a substantial following, including the work of Y. Toda on categorical refinement of Donaldson-Thomas invariants.
Derived categories of coherent sheaves play a central
role in mirror symmetry. A. Bondal, M. Kapranov and V.
Schechtman interpreted the flop behavior of derived
categories in terms of perverse schobers which are categorical analogs of perverse sheaves introduced by M.
Kapranov and V. Schechtman earlier. Further, W. Donovan and T. Kuwagaki extended homological mirror
symmetry to a certain class of perverse schobers. Working with Y. Soibelman and L. Soukhanov, M. Kapranovinterpreted the Algebra of the Infrared of GaiottoMoore Witten in terms of Fourier transform of perverse
schobers.
4. Executing projects successfully to produce worldcompetitive results on dark energy, dark matter, andinflation
LiteBIRD is in the concept design phase and the teamsuccessfully pushed the projects forward under the
new standard. The international partners, including
CNES from France and ASI from Italy, have started their
Phase-A. The US team is supported by the NASA Technology development funding. Progress on various science and technological fronts has been shared over
online meetings. Even with limited access to the lab,the LiteBIRD team presented 13 instrumental development-related presentations and proceedings (4 arefrom Kavli IPMU lead projects) at the online SPIE conference 2020. In relation to the demanding calibration
requirement to the polarization angle, Y. Minami and E.
Komatsu have developed the technique to extract
both the cosmological birefringent rotational angle
and the instrumental angle offset simultaneously.
The HSC papers published in PASJ received a lot of
attention from the community, and contributed to thehighest impact factor PASJ has ever achieved. The HSC
cosmology paper from the cosmic weak lensing power
spectra was awarded the 2020 PASJ excellent paper
award. Our particle physicists and cosmologists proposed a scenario that primordial black holes (PBHs)
were produced by nucleation of false vacuum bubbles
during inflation. They showed that the multiverse PBH
scenario can explain the total amount of dark matterand the possible event of PBH microlensing observedin HSC data. This work benefits from the synergy of awide range of expertise available at the Kavli IPMU.
The instrumentation of PFS is in the phase to actively
integrate and test the hardware and software of thesubsystems. In Sep 2020, all 2394 “Cobra” robotic fiber
positioners were fully installed over the focal plane ofPrime Focus Instrument (PFI). The first fiber cable connecting PFI and Spectrograph System was delivered to
Subaru and was successfully installed in Feb. 2021. The
PFS team managed to install a dedicated little telescope system on the Subaru Telescope that feeds lightfrom the sky to the PFS fiber cable and the spectrograph module. They plan to start on-sky engineeringobservations from fall 2021. In parallel to these instrumentation activities, the PFS science working group,
led by the co-chairs M. Takada and R. Ellis (UCL), hasbeen working on the PFS SSP survey design and feasibility studies in three scientific themes: cosmology,
Galactic archaeology and galaxy evolution.
In April 2020, T2K published results on the measurement of the parameter that governs CP violation in
neutrino oscillations in the journal Nature of which thecorresponding author is M. Hartz. The measurementshows a preference for significant CP violation,although additional data will be necessary to exclude
CP conservation and precisely measure the parameter.
The paper was closely followed by the presentation of
new T2K oscillation measurement results at the Neutrino 2020 with data collected through the beginning of
2020. This year also saw the addition of gadolinium(Gd) sulphate to the SK detector. After ten years oflarge-scale R&D studies on Gd in the 200-ton EGADS

Kavli IPMU Annual Report 20205

Introduction

Introduction

water Cherenkov detector located in the Kamioka
mine, which is led by M. Vagins, the first batch of ultrapure gadolinium sulfate octahydrate was dissolved in
the 50 kilotons of water inside SK. The Gd ions now
present in the detector allow us to easily observe andrecord approximately 50% of the previously invisible
neutrons generated by various physics processes
involving neutrinos, muons, and radioactive decays.
While the J-PARC accelerator will soon go into a long
shutdown for upgrades, T2K is collecting data in Marchand April of 2021 in order to have the first accelerator
neutrino data with Gd in SK.
The Hyper-K project looks forward beyond T2K to makeprecision neutrino oscillation measurements, including
CP violation, nucleon decay searches and supernova
neutrino detection among a broad physics program.
With the approval of the Hyper-K project in 2020, construction has begun, starting with the entrance yard to
the mine where Hyper-K will be located. M. Hartz, isleading the Intermediate Water Cherenkov Detector(IWCD) effort within Hyper-K. The IWCD will be a kiloton scale water Cherenkov Detector located within
1km of the neutrino source at J-PARC in order to makeprecise measurements of neutrino-nucleus scattering
necessary to reduce systematic uncertainties for HyperK. In 2020, the IWCD effort has focussed on internal
documentation and review of the IWCD, with the
preparation of a technical design report, and presentations at Hyper-K Project Advisory Committee meetings.
The XENON collaboration is currently in the process ofcommissioning the XENONnT detector, an upgrade of
the XENON1T detector at the Laboratori Nazionali delGran Sasso in Italy. They expect to start a first science
data run shortly with the upgraded detector, whichcontains over 8 tons of liquid xenon, out of which about
4 tons constitute the target mass. The collaboration’s
ambition to directly detect dark matter particles has
uncovered an intriguing excess of low-energy electron
recoil events in its XENON1T data. Studying this excess
under the significantly improved conditions that the6

Kavli IPMU Annual Report 2020

upgraded detector offers has become another important goal for XENONnT’s upcoming first science datarun.
Upon the start of the Belle II data taking, the Kavli IPMU
team converted its role to Belle II data analysis. They
used 2019 and 2020 for analysis-tool development anddetector-signal calibration for their use for all the future
CP-asymmetry measurements and publications with
the Belle II dataset. The results of the calibration were
published. They will publish physics results with thetools and calibrated results from 2021, starting with the0 –0measurements of the B-meson lifetime, B -B mixing
parameter followed by the CP-asymmetry measure00ment in the B → J/ψK decay. In parallel to the Belle IIdata analysis, they searched for new physics with thefull Belle dataset, which is seven times larger in size
than the current Belle II. The CP asymmetry was consistent with the Standard Model prediction, and they
concluded no evidence for new physics there. They are
finalizing the measurement of the CP-violating phase
φ2 and the search for an invisible gauge boson Z’.
5. Attracting and retaining the best and broadly
minded scientists from around the world
From the developing stage, we had a firm belief thatthe key to gaining international recognition is to bring
together top-level leaders and talented young
researchers worldwide, and create an environment
where researchers in different fields learn each other's
way of thinking and work together toward common
goals. We have established such a fascinating research
environment here at the Kavli IPMU. It functions as thecenter for “brain circulation”. The total number of Principal Investigators (PIs) is 28, among which 11 are on-site
PIs. All of our 28 PIs (7 non-Japanese: 25%) are worldleading scientists and ensure an international environment for research activities at the Kavli IPMU. T. Takahashi is performing a new interdisciplinary activity,
applying hard X-ray and gamma ray detectors hedeveloped to biomedical research. On-site PIs in mathematics, M. Kapranov, Y. Toda, and H. Nakajima, are dis-tinguished mathematicians and research leaders inalgebraic variety, derived category, and gauge theories.
K. Martens was appointed the first non-Japanese Director of the Kamioka-branch, demonstrating the Kavli
IPMU has established a truly international environmentand support system. Other faculty members also playleading roles in each field including PIs of big international projects such as Belle II, T2K, EGADS, HSC, PFS,
and LiteBIRD. Our former PI K. Nomoto was awarded
the Order of the Sacred Treasure. Another former PI T.
Yanagida was awarded the particle physics medal ofJapan. Our former faculty member C. Schnell and anaffiliate member A. Kusenko were selected as Simons
Fellows in 2021.
Our policy for mobilizing and circulating the world’s
best brains is to recruit the brightest young people as
post-doctoral researchers and provide them with thebest research environment to realize outstanding
accomplishments during their three-year term at the
Kavli IPMU. These post-doctoral researchers havebecome strong candidates for either faculty positions
or other post-doctoral positions at prestigious research
institutions. Every year we have about 700 applications
on average, mostly (90%) from abroad. We have beenable to recruit postdocs from many top-level research
institutions in the world, such as Harvard, Princeton,
MIT, etc. By the end of FY 2020, we employed 242 postdocs, and 193 had left the Kavli IPMU, some before thethree-year term expiration. Some postdoc researchers
who have left the Kavli IPMU have found faculty positions at many top-level institutions: Durham U., McGill
U., Stony Brook U., ICRR, Osaka, and CNRS. Others havefound another postdoc position at prestigious institutions: Oxford, Harvard, MPI, Caltech, CERN, YITP, and
KEK, etc. The number of researchers currently in a faculty position became 115 in FY 2020. Also, 47 postdocs
affiliated with us were supported by the JSPS Postdoctoral Fellowship.

6. Bringing successful system reforms to the rest of
the University and other research institutions to help
boost the overall competitiveness of Japan on a
global scale
The Kavli IPMU has led system reform in not only the
University of Tokyo (UTokyo) but also National Universities at large. We made split appointments possible withinstitutions inside and outside Japan. We offer meritbased salaries. The Kavli IPMU has employed the socalled “nenpo system”, improving the mobility of themembers. Kavli IPMU administrative staff members
have been awarded the UTokyo’s Special Prize for Business Transformation by the President six times andtheir development products have been requested byother organizations in the UTokyo.
We take the role of an evangelist to make these reforms
permeate the system to boost the overall competitiveness of research in Japan. One of the examples we haveachieved to spread these reforms can be seen in the
Administrative Director T. Haruyama’s contribution to
Tokushima University on the program established by
the Cabinet Office project “Promotion of Regional
Industries and Universities”. He gave a lecture to the
President and board members of Tokushima University
on the detailed successful experience of the WPI program at the Kavli IPMU. He has been assigned as amember of the External Evaluation Committee of the
newly established laboratory at the university.
7. Making a serious attempt to create a new international graduate program with vigorous student
exchanges
We have also made an impact on the globalization of
the graduate programs at UTokyo. Our faculty has
already contributed to the graduate programs at the
Department of Physics and the Department of Mathematical Sciences through the supervision of graduate
students and lectures voluntarily. We partnered in two
Programs for Leading Graduate Schools, one for “Frontiers of Mathematical Sciences and Physics” (FMSP) andthe other “Advanced Leading Graduate Course for Pho-

Kavli IPMU Annual Report 20207

ton Science” (ALPS). It offers opportunities for interdisciplinary research to UTokyo graduate students in ourinternational and interdisciplinary environment. In
addition, our international faculty lectures on scientificwriting in English in the Department of Physics, a very
popular course among graduate students. So far, morethan 110 students have taken the course.
Faculty members of the Kavli IPMU supervised doctoral
students in astrophysics or particle physics at the University of Oxford to conduct joint research. To date, wehave accepted nine students and five have defended
their Ph.D. theses. For example, L. Cook, who was also a
joint Oxford/Kavli IPMU graduate student, is developing atmospheric neutrino production modeling methods that build on techniques used by the T2K experiment. His work is set to play a key role in the future
neutrino oscillation measurements that combine
atmospheric and accelerator neutrino data. T. Ghigna,
another joint Oxford/Kavli IPMU graduate student,
received his Ph.D. in 2020 and became a Kavli IPMU
postdoc now.
A new graduate program, which was coordinated by H.
Murayama and involved departments of physics, mathematics, astronomy, etc., of UTokyo, was as one of the
JSPS WISE Program (Doctoral Program for World-leading Innovative & Smart Education). This program trains
graduate students in physics, mathematics, and astronomy for diverse career opportunities. Also, it gives us
leverage so that more Kavli IPMU faculty members candirectly supervise graduate students.
8. Enlarging the force for outreach to young students,
by organizing workshops for scientists and highschool teachers
The Kavli IPMU has been extremely active in the outreach to the general public and high-school students.
During the COVID-19 pandemic, we have continued
outreach activities online.
We held an online talk series by four researchers featured in the Kavli IPMU Monoshiri Newspaper, which isa wall newspaper by the Kavli IPMU and aims to pres-8

Kavli IPMU Annual Report 2020

ent easy-to-digest physics and mathematics talks thatcan be enjoyed by all, including people without a background in science. Each introduced research from theirpersonal experience for around 30 minutes for juniorand senior high school students and adults to enjoy thepresentations remotely.
The Kavli IPMU and the Japan Association of Communication for Science and Technology (JACST) presented
an online talk by Y. Toda, titled “Fundamental Talks,
Vol.01: Mathematics – how to interact with objects in
non-everyday manner”. Fundamental Talks is to be a
10-part series of seminars. Researchers from cuttingedge science, social sciences and contemporary art willbe speakers for the events.
We hold a Kavli IPMUxICRR joint general lecture every
year. The lecture in 2020 was “Explorations of theunknown and outer-most limits of the Universe and as
New Physics” online for the audience of junior highschool students and above. H. Takeo talked about the
Belle II experiment and N. Koji (Associate Professor of
ICRR) talked about gamma-ray bursts seen from theground. We held another online Kavli IPMU x ICRR Joint
Public Lecture: “New era of Space telescopes”, where H.
Tagoshi (ICRR) and J. Silverman gave lectures for juniorhigh school students and above. We held the 6th Kavli
IPMU, ELSI, and IRCN Joint Public Lecture online: “A
Question of Origins”. K. Fujishima (ELSI), H. Miyamoto,(IRCN) and T. Watari delivered public lectures for highschool students and above online. Moderated by apolitical science expert, the discussion also touched on
cutting-edge scientific research and the theme, “Whatdoes it mean to ask a question of origins?”.
We held an online screening of the film “Secrets of the
Surface: The Mathematical Vision of Maryam
Mirzakhani” illustrating the life and mathematical workof Maryam Mirzakhani, the first woman and the first
Iranian to be honored with the Fields medal. We invited
the Film Director George Csicsery and other specialists
on Mathematics including M. Yamazaki and had a panel
discussion.

9. Attaining sufficient stability of the organization sothat we can bring our research objectives beyond the
WPI funding
At the time of the original proposal, UTokyo mademany exceptions to the Kavli IPMU as a “special district”
within the University: flexible salary system, longer
appointments than traditional fixed-term positions,moving some PIs with advantageous arrangementswith retirements from traditional departments,
employment after retirement, etc. UTokyo also committed to building the main research building specifically for the Kavli IPMU and a new international lodge
near the Kashiwa campus, which became a main residential facility for international researchers who have
moved to the Kavli IPMU, and short-term visitors. Afterthe Kavli IPMU was established, it also provided extra
assistant professor positions to aid PIs to be freed fromduties to be involved in research at the Kavli IPMU. Former UTokyo President J. Hamada decided to accept
Kavli's donation despite some concerns and opposition within the University.
The creation of TODIAS (later UTIAS) in 2011 is an outstanding support, providing a permanent place for the
Kavli IPMU within the University. Under this structure,
UTIAS requested funding to MEXT to sustain the activity and won 13 permanent positions in UTIAS in 2017.
Following the interim evaluation, UTokyo made several
measures to make the Kavli IPMU sustainable. Finally,
the University provided the Kavli IPMU with 10 tenure
positions at the President's discretion. The University
also secures nine people from the administrative
bureau of the University. During the WPI program committee meeting in 2020, President M. Gonokami
declared that “we will maintain IPMU as our permanent
institute at its current high level of activities, after the
WPI program support ends” by strengthening the Kavli
Foundation fund, and securing budget request for permanent institute. The success of the Kavli IPMU has
given credibility to UTokyo, a bond which is secured by
the value of knowledge obtained by university
research.

OthersAlthough our activity faces various challenges due tothe COVID19, we have carried out various initiatives toencourage communication for mutual inspiration
between different disciplines and to push our projects
forward under the new standard. Instead of our daily
teatime for informal interactions, we hold Kavli IPMU
social hour in a virtual space. Precious lessons we havelearned on how to utilize virtual spaces will help us
work more efficiently and build stronger international
connections, even after the pandemic ends. Almost all
conferences and seminars were held online. In FY2020,
we had 1465 participants for online conferences and
777 foreigners among them. We also had more than
100 seminars online, obtaining about 3000 participants. We started a new colloquium-style webinar
series by Kavli IPMU postdocs to understand each fieldand each other. 7 astronomers, 10 theoretical physicists, and 4 mathematicians gave talks on their researchat the postdoc colloquia. We recruited six short-term
postdocs, “Postdocs en passant”, who could not moveto their new appointments due to visa/travel restrictions but could come to Japan.
Director H. Ooguri has introduced several measures toimprove our diversity, including bias training for the
search committee, revision of harassment training, bestpractices for selections and recruitments, and diversity
requirements on workshops. We have a weekly women’s lunch and provide leadership opportunities forfemale and international scientists. We also establishedour code of conduct. This has inspired UTokyo to establish its code of conduct.

Kavli IPMU Annual Report 20209

Introduction

300

273

285

297

300

Total Number of Staff
329
320
311 318RESEARCH ACTIVITIES

247

250

230

1200

202

200

165

100

80
50

21
18
0 3

194

209

236

245

255

259

252

274

279

280

291

63
10
7

22
11

27
10

30
10

32
10

31
10

29
10

27
10

28
11

29
11

27
11

0

Oct. 2007 Mar. 2008 Mar. 2009 Mar. 2010 Mar. 2011 Mar. 2012 Mar. 2013 Mar. 2014 Mar. 2015 Mar. 2016 Mar. 2017 Mar. 2018 Mar. 2019 Mar. 2020 Mar. 2021

18
0
3
21

63
10
7
80

125
22
11
158

165
27
10
202

194
25
11
230

209
28
10
247

236
27
10
273

245
30
10
285

255
32
10
297

259
31
10
300

252
29
10
291

RESEARCHERS

274
27
10
311

279
28
11
318

280
29
11
320

291
27
11
329

Percentage of Overseas

300

250

44%
52%

200

56%
150

478

600

28
10

35%
41%
40% 41%

38%
98
79

105

90

41% 49% 42%

372
103
168
65
103

432
345

269

103
269
372

345
87
432

0

Overseas
Domestic% of Overseas% of Female

10

65

738

505

464

560

463

384

238

777*

436
688*

338

473

457

465
296

264

302

446

478
384
862

392
238
630

497 544 471 505 464
338 473 457 296 264
835 1,017 928 1,801 728

436 560 463 777*
302 465 446 688*
738 1,025 909 1,465*

SEMINARS & CONFERENCES

46%

300

250

111

136

118

135

102

200

131

147

150

169

150

163

143

162

186

156

156

94

50

0

Oct. 2007 Mar. 2008 Mar. 2009 Mar. 2010 Mar. 2011 Mar. 2012 Mar. 2013 Mar. 2014 Mar. 2015 Mar. 2016 Mar. 2017 Mar. 2018 Mar. 2019 Mar. 2020 Mar. 2021

51760
92 100 79 105 98 105 90 102 111 136 118 135
13 46
65
73 94 130 131 147 150 169 150 163 143 162 156
28% 28% 48% 56% 52% 38% 44% 40% 41% 35% 41% 41% 49% 42% 46%
0% 2% 5% 6% 5% 2% 5% 5% 6% 4% 6% 8% 9% 10% 9.3%

Kavli IPMU Annual Report 2020

497

150

130

728

471

Multiple visits in a given year are counted as one.
* Number of participants for online conferences in 2020

100

73

630

105

60

28%
17
50
28% 46
18
3

801

392

87

92
100

909

FY 2007 FY 2008 FY 2009 FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020

Visitors (Overseas) 65
Visitors (Domestic) 103
Visitors (Total)
168

100

48%

835
544

300

25
11

928

862

900

125

27
10

1,025

1,017

158

150

Researchers
Research Support Staffs
Administrative staffs
Total

1,465*

1500

291

Introduction

STAFF

Seminars
Conferences

196

232

249

246

222
184

192

216

207

140
116

24
4

7

11

16

12

11

14

13

17

14

11

21

18

8

FY 2007 FY 2008 FY 2009 FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020

24
4

156
7

140
11

186
16

196
12

232
11

249
14

246
13

222
17

184
14

192
11

216
21

207
18

116
8

Kavli IPMU Annual Report 202011

Introduction

PUBLICATIONSTOTAL EXPENDITURE(1,000,000 JPY)(%)

589 100

600
550

519

500

480

450

68

400
350

347

350

67

449

78

449

422

81

79

80

236

80
70
60

252

40

202

200

30

150

115

100

2,707

2,362
1,524

1500 1,366

896

10

9

0

Publications
9
115 202% of international collaboration 49% 57%

0

25
25
288
132

425
92

933

5,581

5,454

227

366
163
135
119
16

182

167

170

195

153
29

137
30

143
27

161
34

541

635

Kavli IPMU Annual Report 2020

90

486

486

444

825

906

987

1,027

1,101

93

397
91

387
82

653

574

619

295
104

1,023

1,006

948

2,513
391

335
119

268
98

494

411

265
18
553

1,310

1,357

1,286

408

925

BREAKDOWN OF FY 2020 TOTAL EXPENDITURE

203

391
15.6 %
265
10.5 %

379
157

551

316

318

392
174

173
304

222

143

1,286
51.2 %

18
0.7 %

3000

553
22.0 %

2000
1000

223

218

FY 2007 FY 2008 FY 2009 FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020

participants in outreach activities
media coverages (domestic)
media coverages (international)

96

453

388

4000

531

3,277

130
47
97
40 0
33
0 7

489

231
80
234

5000

4,764 382

3,339 3,340

200

538

117
88
404

6,296 6000

1,376

1,259

730

6,232

1000

400

783

846

2,864

7000

6,084

600

1,024

7,540

7,018

4,545

1,301

2,991 3,041

FY 2007 FY 2008 FY 2009 FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020

MEDIA COVERAGES AND OUTREACH ACTIVITIES

800

1,225

1,866

Personnel
Project Activities
Travel Expenses
Equipment
Other Research Project236 252 347 350 480 449 449 422 519 496 589
68% 60% 67% 69% 67% 75% 78% 78% 81% 79% 80%

1200

500

48
112

911

3,262
1,842

1,410

2000

1000

2,844

2,844

2500

20

FY 2007 FY 2008 FY 2009 FY 2010 FY 2011 FY 2012 FY 2013 FY 2014 FY 2015 FY 2016 FY 2017 FY 2018 FY 2019 FY 2020

12

3000

50

250

0

69

78

496

49

300

50

60

57

67

75

90

3,372 3,425

3500

Introduction

3,910 3,902

0(1,000,000 JPY)
Personnel
Project Activities
Travel Expenses
Equipment
Other Research Project

Kavli IPMU Annual Report 2020

13

APRIL>> Researchers pin down a quantum mechanicalanomaly in electromagnetism>> Belle II explores new “portal” into dark matter - First
results from the Belle II experiment>> T2K results restrict possible values of neutrino CP
phase>> Kavli IPMU senior scientist Ken’ichi Nomotoawarded the order of the sacred treasure

MAY>> Hyper-K technical coordination meeting (Online)>> Kavli IPMU Monoshiri Journal online talk series (May30-31)

JUNE>> The origin of Type Ia supernovae revealed bymanganese abundances>> Observation of excess events in the XENON1T dark
matter experiment>> Researchers find the origin and the maximum massof massive black holes observed by gravitational
wave detectors

14

Kavli IPMU Annual Report 2020

April 2020 - March 2021

JULY>> McKay correspondence, mutation and related
topics (Online)

AUGUST>> Fundamental Talks (Online), Vol. 01: Mathematics—
how to interact with objects in a non-everyday
manner>> Fundamental Talks (Online), Vol. 02: What we talkabout when we talk about color quality for science,art or philosophy>> Kavli IPMU x ICRR joint public lecture:“Explorations of the unknown and outer-most limitsof the universe and a new physics”>> An international research team analysis rules out
dark matter destruction as origin of extra radiationin galaxy center>> Rare encounters between cosmic heavyweights

SEPTEMBER>> WPI site visit>> Research suggests our galaxy’s brightest gammaray binary system may be powered by a magnetarstar>> Kavli IPMU’s Tsutomu Yanagida awarded 20th
particle physics medal of Japan>> Beauty 2020 (Online)>> Science cafe “Universe”

OCTOBER>> The Kavli Foundation in the United States receives
the University of Tokyo’s Shokumon Award>> History of temperature changes in the universe
revealed—First measurement using the SunyaevZeldovich effect>> Study of supergiant star Betelgeuse unveils thecause of its pulsations; Recalibrated its mass, radius,and distance>> Kashiwa campus open day, 2020>> Looking for dark matter near neutron stars withradio telescopes>> Galaxies in the infant universe were surprisingly
mature -ALMA telescope conducts largest survey
yet of distant galaxies in the early universe>> Primordial black holes and the search for dark
matter from the multiverse

NOVEMBER>> The world of mathematical physics (Online)>> 5th “Actually I really love physics!”–Career paths offemale physics graduates (Online)>> Secrets of the surface online film screening + panel>> Kavli IPMU x ICRR joint public lecture: “New era ofspace telescopes”>> A hint of new physics in polarized radiation fromthe early universe>> Researchers validate theory that neutrinos shape
the universe>> CMB systematics and calibration focus workshop(Online)

DECEMBER>> Science cafe “Universe”>> Kavli IPMU annual report 2019 released>> Principal Investigator David Spergel electedpresident of Simons Foundation>> World-class researchers are coming from WPI!
(Online Event)>> American astronomers find secrets of Japanese
universes

News & Events

2

NEWS & EVENTSNews & Events

JANUARY>> The smallest galaxies in our universe bring more
about dark matter to light>> Time-domain cosmology with strong gravitational
lensing (Online)

FEBRUARY>> Chiaki Hikage and others win the 2020 PASJ
excellent paper award>> Kavli IPMU visiting senior scientist Alexander
Kusenko and visiting scientist Christian Schnell
selected as 2021 Simons Fellows>> What is dark matter? - Comprehensive study of thehuge discovery space in dark matter (Online)>> WPI science symposium 2021 “Life” in the 21st
century>> Establishing the origin of solar-mass black holes
and the connection to dark matter>> The 6th Kavli IPMU, ELSI, and IRCN joint public
lecture: “A Question of Origins”

MARCH>> 12th PFS collaboration meeting (Online)>> Social context affects gendered views of STEM
subjects in England and Japan -New model of why
physics and mathematics are seen as masculine
subjects>> String theory solves mystery about how particles
behave outside a black hole photon sphere

Kavli IPMU Annual Report 202015

Kavli IPMU

Kavli IPMU Management

President

Makoto Gonokami

UTIAS

Director

Director: Masashi Haneda

Kavli IPMU External
Advisory Committee

Hirosi Ooguri

Administrative
Director

Deputy Directors

Tomiyoshi Haruyama

Assistant Administrative
Director

Hiroaki Aihara
Misao Sasaki
Tomiyoshi Haruyama

Junichi Kanzaki

Steering Committee

The Kavli IPMU has a rather unique organization. While
research is conducted in a flat-structure manner with loosely
defined grouping, the decision making is done in a top-down
scheme under the Director’s strong leadership. This scheme
minimizes the administrative load for the researchers. It is also
intended to maximally extract young researcher’s creativeand challenging minds as well as to encourage daily crossdisciplinary interactions.
The Director is appointed by the President of the University ofTokyo and reports directly to his office. The Director proposes
to hire the Principal Investigators to the President. For otherhiring of research staff and administrative staff, he has a complete authority. He is also solely responsible for making allother decisions. He is assisted by the three Deputy Directors
and the Administrative Director. They constitute the Executive Board (EB) and regularly meet to ensure smooth operation of the Institute. The EB has direct access to the Office of
the President for consultations on both scientific and administrative matters.

The Director is obliged to report the appointments of new
Principal Investigators and faculty members to the Director of
the University of Tokyo Institutes for Advanced Study (UTIAS).
Also, to clear the university formality in faculty hiring, the decisions of the Institute have to be endorsed by the Steering
Committee of the Kavli IPMU.
The Principal Investigators are world’s leading scientists intheir fields. They have a large autonomy in the research they
conduct. They can make proposals to the Director to hire
research staff at the Institute.

Organization

3

ORGANIZATION

Organization

The External Advisory Committee (EAC), appointed by the
President of the University of Tokyo, reviews annually the scientific achievement and activities of the Institute and advises
the President on scientific priorities and the research activities
to keep the Institute stay on the course of its objectives.

Executive Board
Chair

Hirosi Ooguri
Hiroaki Aihara
Misao Sasaki
Tomiyoshi Haruyama
		Mikhail Kapranov
Masahiro Takada
Mark Vagins
Hiromi Yokoyama

Director
Deputy Director
Deputy Director
Administrative Director/Deputy Director
Principal Investigator
Principal Investigator
Principal Investigator
Professor

The External Advisory Committee Members (March 2021)
John Ellis
Giovanni Felder
Joshua Frieman
Masahiko Hayashi
Tatsuya Nakada
Yongbin Ruan
Sakura Schafer-Nameki
Nigel Smith

King's College London
ETH Zürich
FNAL/U Chicago; Chair
JSPS Bonn Office
EPFL
Zhejiang University
U Oxford
SNOLAB

Particle Theory
Mathematics
Astrophysics
AstronomyHigh Energy Experiment
Mathematics
Mathematical Physics
Astroparticle Physics

Kavli IPMU Research

Principal Investigators
Faculty, Postdocs, Students, Visitors

16

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202017

Organization

experiments conducted at the Kamioka underground laboratory. The Berkeley Satellite, besides being a place forresearch, serves as a contact place to the US scientific community. We also have close collaborative relations with several institutions both in Japan and overseas as well as withother departments within the University of Tokyo.

The Kavli IPMU holds close relations with similar research
institutions in the world for encouraging exchanges in
research and training of young research staff. We have signed
either an agreement or a memorandum of understanding
with those institutions.

Foreign institutions/consortia/programs having MOU with the Kavli IPMU

Host InstituteCollaborating Institutions(The Univ. of Tokyo)(domestic)

National Astronomical
Observatory in Japan Department of Mathematics
 Institute for Cosmic Ray Research(Kashiwa, Kamioka) Department of Physics
 Department of Astronomy

Collaborating Institutions(overseas)

Department of Physics,
University of California, Berkeley, USA
Department of Astrophysical Sciences,
Princeton University, USA
Institut des Hautes
Etudes Scientifiques (IHES), France

18

Kavli IPMU Annual Report 2020

Kavli IPMU
Kashiwa Campus
Kamioka Branch

Berkeley
Satellite

Department of Physics,
Kyoto University
High Energy Accelerator
Research Organization (KEK)
Yukawa Institute for
Theoretical Physics,
Kyoto University

The University of California, Berkeley, Department of Physics
National Taiwan University, Leung Center for Cosmology and Particle Astrophysics (LeCosPA)
The Astrophysics Research Consortium [on the Sloan Digital Sky Survey III ]The Astrophysics Research Consortium [on the Sloan Digital Sky Survey AS3 (“After SDSS III”)]
The Astrophysics Research Consortium [on the Sloan Digital Sky Survey IV ]Garching/Munich Cluster of Excellence on “The Origin and Structure of the Universe”
UNIFY (Unification of Fundamental Forces and Applications) [under the EU’s Seventh Framework Program]
The Scuola Internationale Superiore di Studi Avanzati (SISSA)The Academia Sinica Institute of Astronomy and Astrophysics of Taiwan (ASIAA) [on the SuMIRe Project]
The Intermediate Palomar Transient Factory (iPTF)
Steklov Mathematical Institute, Russian Academy of Sciences
Center for Mathematical Sciences, Tsinghua University
The Tata Institute of Fundamental Research
TRIUMF (Canada’s National Laboratory for Particle and Nuclear Physics)
Deutsches Elektronen Synchrotron (DESY)
Princeton University
The University of Oxford, Department of Physics
The Kavli Institute for Astronomy and Astrophysics at Peking University (KIAA)
Le Centre National de la Recherche Scientifique (CNRS)The Mainz Institute for Theoretical Physics (MITP)
Johns Hopkins University
The University of Bonn

Organization

The main laboratory building on the Kashiwa Campus provides a basis for our researchers. Even most of experimentalists who are involved in Kamioka experiments and astronomical observations spend a good fraction of their time in
Kashiwa for analyzing data, sharing seminars and discussing
with theorists. The Kamioka Branch is a basis for the Kavli
IPMU staff members who are engaging in the undergroundResearch Center for
Neutrino Science,
Tohoku University
Institiute of Physical andChemical Research (RIKEN)
Institiute of Statistical
Mathematics (ISM)

Kavli IPMU Annual Report 2020

19

4

STAFF
Naoshi Sugiyama (Nagoya U), Cosmology
Masahiro Takada, Cosmology
Tadayuki Takahashi, Experimental Physics
Yukinobu Toda, Mathematics
Mark Robert Vagins, Astroparticle Physics
Naoki Yoshida (U Tokyo), Astrophysics

Faculty Members

Kavli IPMU 13th Anniversary

Director
Hirosi Ooguri, Mathematical Physics

Deputy Directors
Hiroaki Aihara, High Energy Physics
Tomiyoshi Haruyama, High Energy Physics
Misao Sasaki, Cosmology

Principal Investigators
Hiroaki Aihara (U Tokyo), High Energy Physics
Alexey Bondal (Steklov Math. Inst.), Mathematics
Kentaro Hori, String Theory
Kunio Inoue (Tohoku U), Neutrino Physics
Takaaki Kajita (U Tokyo, ICRR), Neutrino Physics
Mikhail Kapranov, Mathematics
Stavros Katsanevas (European Gravitational Observatory),

20

Kavli IPMU Annual Report 2020

Experimental Physics
Masahiro Kawasaki (U Tokyo, ICRR), Cosmology
Young-Kee Kim (U Chicago), High Energy Physics
Toshiyuki Kobayashi (U Tokyo, Math Sci), Mathematics
Toshitake Kohno (Meiji U), Mathematics
Eiichiro Komatsu (MPI for Astrophysics), Cosmology
Kai Uwe Martens, Experimental Physics
Shigeki Matsumoto, Cosmology
Shigetaka Moriyama (U Tokyo, ICRR), Neutrino Physics
Hitoshi Murayama (UC Berkeley), Particle Theory
Masayuki Nakahata (U Tokyo, ICRR), Astroparticle Physics
Hiraku Nakajima, Mathematics
Mihoko Nojiri (KEK), Particle Theory
Yasunori Nomura (UC Berkeley), Particle Theory
Hirosi Ooguri (CALTECH), Mathematical Physics
David Spergel (Princeton U), Cosmology

Tomoyuki Abe, Mathematics
Mark Patrick Hartz, Neutrino Physics
Tomiyoshi Haruyama, High Energy Physics
Simeon John Hellerman, String Theory
Takeo Higuchi, High Energy Physics
Chiaki Hikage, Cosmology
Kentaro Hori, String Theory
Yukari Ito, Mathematics
Mikhail Kapranov, Mathematics
Nobuhiko Katayama, High Energy Physics
Khee-Gan Lee, Astronomy
Kai Uwe Martens, Experimental Physics
Shigeki Matsumoto, Cosmology
Tomotake Matsumura, Experimental Physics
Thomas Edward Melia, Theoretical Physics
Todor Eliseev Milanov, Mathematics
Hitoshi Murayama (UC Berkeley), Particle Theory
Hiraku Nakajima, Mathematics
Hirosi Ooguri (CALTECH), Mathematical Physics
Tadashi Orita, Experimental Physics
Misao Sasaki, Cosmology
Satoshi Shirai, Particle Theory
John David Silverman, Astronomy
Yevgeny Stadnik, Theoretical Physics (from 2020/11/1)
Nao Suzuki, Astrophysics
Yuji Tachikawa, Particle Theory
Masahiro Takada, Cosmology
Tadayuki Takahashi, Experimental Physics
Shinichiro Takeda, Experimental Physics
Naoyuki Tamura, Astronomy
Yukinobu Toda, Mathematics
Mark Robert Vagins, Astroparticle Physics
Taizan Watari, Theoretical Physics
Atsushi Yagishita, Experimental Physics
Masahito Yamazaki, String Theory
Naoki Yasuda, Astronomy
Hiromi Yokoyama, Science and Society
Naoki Yoshida (U Tokyo), Astrophysics
Yutaka Yoshida, String Theory

Project Researchers
Shunsuke Adachi, Experimental Physics (from 2021/3/1)
Kazuyuki Akitsu, Cosmology
Ryosuke Akutsu, Neutrino Physics (2020/5/16-12/15)
Meer Ashwinkumar, String Theory (from 2020/11/1)
Metin Ata, Cosmology

Neil David Barrie, Particle Theory (till 2020/10/15)
Tobias Binder, Theoretical Physics
Connor Hugh Bottrell, Astrophysics (from 2020/10/16)
Yalong Cao, Mathematics
Pietro Caradonna, Experimental Physics
William Richard Coulton, Cosmology (from 2020/10/9)
Thomas Rafael Czank, Experimental Physics
Anton Reyes De la Fuente, String Theory
Zhiyuan Ding, Mathematics
Xuheng Ding, Astronomy (from 2020/9/1)
Matthew Dodelson, String Theory
Joshua Armstrong Eby, Cosmology (from 2020/11/13)
Fatemeh Elahi, High Energy Physics (from 2021/1/14)
Ryo Fujita, Mathematics (2020/8/16-10/6)
Dmitrii Galakhov, String Theory
Hua Gao, Astrophysics (from 2020/11/12)
Tommaso Ghigna, Experimental Physics (from 2020/11/26)
Ryuichiro Hada, Cosmology
Seyed Morteza Hosseini, String Theory
Chang-Tse Hsieh, Theoretical Physics (till 2020/8/31)
Yuko Ikkatai, Science and Society
Hiroaki Imada, Astronomy (2020/6/1-9/30)
Derek Beattie Inman, Cosmology (from 2020/9/16)
Jian Jiang, Astronomy
Ayuki Kamada, Cosmology (2020/11/1-2021/1/31)
Daisuke Kaneko, High Energy Physics (till 2020/7/31)
Miho Katsuragawa, Experimental Physics
Lalitwadee Kawinwanichakij, Astrophysics
Ilya Khrykin, Astrophysics
Robin Rinze Kooistra, Astronomy
Chiara La Licata, Experimental Physics
Yun-Tsung Lai, High Energy Physics (from 2020/6/1)
Chervin Laporte, Astrophysics (till 2021/2/28)
Hsueh-Yung Lin, Mathematics
Wentao Luo, Astrophysics
Oscar Macias , Astrophysics
Ryu Makiya, Astronomy (till 2020/8/31)
Abhiram Mamandur Kidambi, Mathematical Physics(from 2020/11/1)
Frederick Takayuki Matsuda, Experimental Physics
Yuki Moritani, Astronomy
Dinakar Muthiah, Mathematics (till 2021/1/4)
Keigo Nakamura, Neutrino Physics (till 2020/10/31)
Shusuke Otabe, Mathematics
Hyunbae Park, Cosmology
Youngsoo Park, Cosmology
Samuel Charles Passaglia, Cosmology (from 2020/12/14)
Shi Pi, Astrophysics (till 2020/10/24)
Alexis Roquefeuil, Mathematics
Ipsita Saha, Particle Theory
Yuki Sakurai, Experimental Physics
Yuya Sakurai, Astrophysics
Yota Shamoto, Mathematics
Jingjing Shi, Cosmology
Kavli IPMU Annual Report 2020

Staff

Staff

21

Yevgeny Stadnik, Theoretical Physics (till 2020/10/31)
Satoru Takakura, Astronomy
Volodymyr Takhistov, Theoretical Physics (from 2020/10/1)
Tomohiko Tanabe, Particle Theory (from 2021/1/1)
Ryota Tomaru, Experimental Physics (till 2020/9/30)
Daisuke Toyouchi, Astronomy (from 2020/10/16)
Izumi Umeda, Medical Application of Gamma-ray Imaging
Valeri Vardanyan, Cosmology
John Welliaveetil, Mathematics
Graham Albert White, Particle Theory (from 2020/8/1)
Kenneth Christopher Wong, Astronomy
Kiyoto Yabe, Astronomy
Ryo Yamagishi, Mathematics
Hassen Yesuf, Astronomy (from 2021/3/1)
Wai Kit Yeung, Mathematics (from 2020/6/16)
Yunqin Zheng, Theoretical Physics (from 2020/11/5)
Zijun Zhou, Mathematics (from 2020/11/16)

Joint Appointments
Mark Patrick Hartz (TRIUMF), Neutrino Physics
Masashi Hazumi (KEK), High Energy Physics
Hitoshi Murayama (UC Berkeley), Particle Theory
Hirosi Ooguri (CALTECH), Mathematical Physics
Naoki Yoshida (U Tokyo), Astrophysics

Affiliate Members
Kou Abe (U Tokyo, ICRR), Astroparticle Physics
Mina Aganagic (UC Berkeley), String Theory
Shin’ichiro Ando (U Amsterdam), Astroparticle Physics
Bruce Berger (Lawrence Berkeley National Laboratory),
Neutrino Physics
Melina Bersten (IALP CONICET-UNLP), Astronomy
Sergey Blinnikov (ITEP), Astronomy
Agnieszka Maria Bodzenta-Skibinska (U Warsaw),
Mathematics (from 2021/2/1)
Raphael Bousso (UC Berkeley), Cosmology
Kevin Allen Bundy (UC Santa Cruz), Astronomy
Andrew Bunker (U Oxford), Astrophysics
Martin Gilles Bureau (U Oxford), Astronomy
Scott Huai-Lei Carnahan (U Tsukuba), Mathematics
Cheng-Wei Chiang (Natl Taiwan U), Particle Theory
Yuji Chinone (U Tokyo), Astronomy
Neal K Dalal (Perimeter Institute), Astrophysics
Patrick Decowski (U Amsterdam/GRAPPA), Neutrino Physics
Jason Detwiler (U Washington, Seattle), Neutrino Physics
Mamoru Doi (U Tokyo, IoA), Astronomy
Chris Done (Durham U), Astrophysics
William Ross Goodchild Donovan (Tsinghua U, Beijing),
Mathematics (from 2020/9/1)
Yuri Efremenko (U Tennessee), Neutrino Physics
Motoi Endo (KEK), Particle Theory
Sanshiro Enomoto (U Washington, Seattle), Neutrino Physics
Andrea Ferrara (Scuola Normale Superiore di Pisa),
Astronomy

22

Kavli IPMU Annual Report 2020

Gaston Folatelli (IALP CONICET-UNLP), Astrophysics
Andreu Font-Ribera (IFAE-Barcelona), Cosmology
Brian Fujikawa (LBL, Berkeley), Neutrino Physics
Kenji Fukaya (SCGP), Mathematics
Masataka Fukugita (U Tokyo), Astrophysics
Shao-Feng Ge (Shanghai Jiao Tong U), Theoretical Physics
Lawrence J Hall (UC Berkeley), Particle Theory
Koichi Hamaguchi (U Tokyo), Particle Theory
Jiaxin Han (Shanghai Jiao Tong U), Astronomy
Tilman Hartwig (U Tokyo), Astrophysics
Tetsuo Hatsuda (RIKEN), Nuclear Physics
Yoshinari Hayato (U Tokyo, ICRR), Neutrino Physics
Karsten Heeger (Yale U), Neutrino Physics
Katsuki Hiraide (U Tokyo, ICRR), Astroparticle Physics
Raphael Hirschi (Keele U), Astronomy
Junji Hisano (Nagoya U), Particle Theory
Petr Horava (UC Berkeley), String Theory
Glenn Horton-Smith (Kansas State U), Neutrino Physics
Shinobu Hosono (Gakushuin U), Mathematical Physics
Kenta Hotokezaka (U Tokyo, School of Science), Astrophysics
Masahiro Ibe (U Tokyo, ICRR), Particle Theory
Koichi Ichimura (Tohoku U), Astroparticle Physics
Hirokazu Ikeda (JAXA), Experimental Physics
Motoyasu Ikeda (U Tokyo, ICRR), High Energy Physics
Shiro Ikeda (ISM), Mathematics
Yoshiyuki Inoue (Osaka U), Astrophysics
Ken’ichi Izawa (Tokushima U), Particle Theory
Nicholas Kaiser (École normale supérieure), Cosmology
Jun Kameda (U Tokyo, ICRR), Neutrino Physics
Yousuke Kanayama (RIKEN), Experimental Physics
Amanda Irene Karakas (Monash U), Astronomy
Masaki Kashiwara (Kyoto U), Mathematics
Akishi Kato (U Tokyo, Math Sci), Mathematical Physics
Yasuyuki Kawahigashi (U Tokyo, Math Sci), Mathematics
Edward T. Kearns (Boston U), Neutrino Physics
Sergey Ketov (Tokyo Metropolitan U), Theoretical Physics
Nobuhiro Kimura (U Tokyo, ICRR), High Energy Physics
Yasuhiro Kishimoto (Tohoku U), Neutrino Physics
Ryuichiro Kitano (KEK), Particle Theory
Chiaki Kobayashi (CAR, U of Hertfordshire ), Astronomy
Kazuyoshi Kobayashi (Waseda U), Astroparticle Physics
Masayuki Koga (Tohoku U), Neutrino Physics
Kazunori Kohri (KEK), Cosmology
Satoshi Kondo (Middle East Technical University),
Mathematics
Yusuke Koshio (Okayama U), Neutrino Physics
Akito Kusaka (U Tokyo), Experimental Physics
Alexander Kusenko (UCLA), Particle Theory
Tatsuki Kuwagaki (Osaka U), Mathematics
Alexie, Solange Leauthaud Harnett (UC Santa Cruz),
Astrophysics
Shiu-Hang (Herman) Lee (Kyoto U), Astrophysics
Si Li (Tsinghua U, Beijing), Mathematical Physics
Marco Limongi (INAF), Astrophysics

Keiichi Maeda (Kyoto U), Astrophysics
Kazuo Makishima (U Tokyo), High Energy Physics
Ryu Makiya (ASIAA), Astronomy (from 2020/9/1)
Brice Menard (Johns Hopkins U), Astrophysics
Makoto Minowa (U Tokyo), Experimental Physics
Makoto Miura (U Tokyo, ICRR), High Energy Physics
Hironao Miyatake (Nagoya U), High Energy Physics
Hiroshi Mizuma (RIKEN), Experimental Physics
Anupreeta Sadashiv More (IUCAA), Astronomy
Surhud Shrikant More (IUCAA), Astronomy
Takeo Moroi (U Tokyo), Particle Theory
Tomoki Morokuma (U Tokyo, IoA), Astronomy
David Robert Morrison (UC Santa Barbara), Mathematics
Shinji Mukohyama (Kyoto U), Cosmology
Motohico Mulase (UC Davis), Mathematics
Dinakar Muthiah (U Glasgow), Mathematics (from 2021/1/5)
Kentaro Nagamine (Osaka U), Astrophysics
Yasuhiro Nakajima (U Tokyo, School of Science),
Neutrino Physics
Kengo Nakamura (Butsuryo College of Osaka),
Neutrino Physics
Kenzo Nakamura (KEK), Neutrino Physics
Tsuyoshi Nakaya (Kyoto U), High Energy Physics
Kazunori Nakayama (U Tokyo), Cosmology
Shoei Nakayama (U Tokyo, ICRR), Neutrino Physics
Yu Nakayama (Rikkyo U), Theoretical Physics
Takahiro Nishimichi (Kyoto U), Cosmology
Ken’ichi Nomoto (U Tokyo), Astronomy
Hirokazu Odaka (U Tokyo), High Energy Astrophysics
Hiroshi Ogawa (Nihon U), Astroparticle Physics
Masamune Oguri (U Tokyo), Cosmology
Shinnosuke Okawa (Osaka U), Mathematics
Kimihiro Okumura (U Tokyo, ICRR), Neutrino Physics
Teppei Okumura (Academia Sinica), Cosmology
Yoshiyuki Onuki (U Tokyo, ICEPP), High Energy Physics
Domenico Orlando (INFN), String Theory
Masaki Oshikawa (U Tokyo, ISSP), Theoretical Physics
Masami Ouchi (U Tokyo, ICRR), Astronomy
Andrei Pajitnov (U Nantes), Mathematics
Myeonghun Park (SEOULTECH), Particle Theory
Serguey Todorov Petcov (SISSA), Particle Theory
Shi Pi (Chinese Academy of Sciences), Astrophysics(from 2020/10/25)
Andreas Piepke (U Alabama), Neutrino Physics
J. Xavier Prochaska (UC Santa Cruz), Astronomy
Anna Puskas (U Queensland), Mathematics
Robert Michael Quimby (San Diego State U), Astronomy
Susanne Reffert (U Bern), String Theory
Jason Rhodes (NASA JPL/Caltech), Cosmology
Joshua Thomas Ruderman (New York U), Particle Theory
Wiphu Rujopakarn (Chulalongkorn U.), Astronomy
Kyoji Saito (Kyoto U), Mathematics
Ryo Saito (Yamaguchi U), Astrophysics

Shun Saito (Missouri U of Science and Technology),
Cosmology
Yoshihisa Saito (Rikkyo U), Mathematics
Yoshio Saito (U Tokyo, ICRR), High Energy Physics
Hidetaka Sakai (U Tokyo, Math Sci), Mathematics
Francesco Sala (U Pisa), Mathematics
Katsuhiko Sato (JSPS), Astroparticle Physics
Vadim Schechtman (U Toulouse III-Paul Sabatier),
Mathematics
Christian Schnell (SUNY, Stony Brook ), Mathematics
Kate Scholberg (Duke U), Neutrino Physics
Hiroyuki Sekiya (U Tokyo, ICRR), Neutrino Physics
Masato Shiozawa (U Tokyo, ICRR), High Energy Physics
Gary Shiu (U Wisconsin, Madison ), String Theory
Aurora Simionescu (SRON Netherlands Institute for Space
Research), Astrophysics
Fedor Smirnov (LPTHE), Mathematics
Michael Smy (UC Irvine), Neutrino Physics
Charles Louis Steinhardt (U Copenhagen), Astronomy
Samantha Lynn Stever (Okayama U), Astrophysics
James L. Stone (Boston U), High Energy Physics
Shigeki Sugimoto (Kyoto U), Theoretical Physics
Toshikazu Suzuki (U Tokyo, ICRR), Gravity
Atsushi Takahashi (Osaka U), Mathematics
Fuminobu Takahashi (Tohoku U), Particle Theory
Tadashi Takayanagi (Kyoto U), String Theory
Atsushi Takeda (U Tokyo, ICRR), Astroparticle Physics
Yasuhiro Takemoto (U Tokyo, ICRR), Experimental Physics
Yasuo Takeuchi (Kobe U), Astroparticle Physics
Hidekazu Tanaka (U Tokyo, ICRR), Neutrino Physics
Masaomi Tanaka (Tohoku U), Astronomy
Atsushi Taruya (Kyoto U), Astrophysics
Takayuki Tomaru (NAOJ), Experimental Physics
Nozomu Tominaga (NAOJ), Astrophysics
Werner Tornow (Duke U), Neutrino Physics
Akihiro Tsuchiya (Nagoya U), Mathematics
Sachiko Tsuruta (Montana State U), Astrophysics
Edwin L Turner (Princeton U), Astrophysics
Kazushi Ueda (U Tokyo, Math Sci), Mathematics
Hokuto Uehara (Tokyo Metropolitan U), Mathematics
Alexander Voronov (U Minnesota), Mathematics
Christopher W. Walter (Duke U), Neutrino Physics
Shin Watanabe (JAXA), Experimental Physics
Bryan Webber (U Cambridge), Particle Theory
Roger Alexandre Wendell (Kyoto U), Neutrino Physics
Marcus Christian Werner (Duke Kunshan U),
Mathematical Physics
Benda Xu (Tsinghua U, Beijing), Experimental Physics
Masaki Yamashita (Nagoya U), Astrophysics
Tsutomu Yanagida (Shanghai Jiao Tong U), Particle Theory
Jun’ichi Yokoyama (U Tokyo, School of Science), Cosmology
Masashi Yokoyama (U Tokyo), High Energy Physics
Shuichiro Yokoyama (Nagoya U), Cosmology

Kavli IPMU Annual Report 2020

Staff

Staff

23

Staff24

Graduate Students

Berkley satellite Members

Administration

Public Relations

Weiguang Cao, Theoretical Physics
Laurence Cook (U Oxford), Neutrino Physics
Henrique De Campos Affonso, Mathematics
Sho Egusa, String Theory
Yuichi Enoki, Particle Theory
Kento Furukawa, Experimental Physics
Tommaso Ghigna (U Oxford), Experimental Physics(till 2020/11/25)
Alexander Goldsack (U Oxford), Neutrino Physics(till 2020/8/31)
Shunichi Horigome, Astroparticle Physics
Yuxin Huang, Astronomy (from 2020/9/1)
Keita Kanno, Particle Theory
Taisuke Katayose, Theoretical Physics
Tenyo Kawamura, Experimental Physics
Tasuki Kinjo, Mathematics
Nozomu Kobayashi, Particle Theory
Yosuke Kobayashi, Cosmology
Asahi Kojima, Particle Theory
Toshiki Kurita, Theoretical Physics
Yasunori Lee, Particle Theory
Xiangchong Li, Cosmology
Peijang Liu , Mathematics
Tianle Mao, Mathematics
Takuro Matsumoto, Mathematics
Takahiro Minami, Experimental Physics
Kairi Mine, Experimental Physics
Yuto Moriwaki, Mathematics
Kai Murai, Particle Theory
Colm Murphy (U Oxford), High Energy Physics
Shunsaku Nagasawa, Experimental Physics
Masato Nakagiri, Mathematics
Shigenori Nakatsuka, Mathematics
Kanade Nishikawa, Particle Theory
Tian Qiu, Cosmology
Yotaro Sato, Theoretical Physics
Yusuke Sato, Mathematics
Yuta Sato, Particle Theory
Ryota Shimoda, Theoretical Physics
Yusuke Suetake, String Theory
Sunao Sugiyama, Theoretical Physics
Shenli Tang, Astronomy
Takanori Taniguchi, Cosmology
Shintaro Toita, Particle Theory
Satoshi Toki, Cosmology
Akira Tokiwa, Cosmology
Yutaka Tsuzuki, Experimental Physics
Yu Watanabe, Particle Theory
Xia Xiaokun, Mathematics
Goro Yabu, Experimental Physics
Chenghan Zha, Mathematics

Mina Aganagic (UC Berkeley), String Theory
Raphael Bousso (UC Berkeley), Cosmology
Lawrence J Hall (UC Berkeley), Particle Theory
Petr Horava (UC Berkeley), String Theory
Yasunori Nomura (UC Berkeley), Particle Theory

Tomiyoshi Haruyama, Administrative Director, Project
Professor
Junichi Kanzaki, Assistant Administrative Director, ProjectLecturer
Isao Uehara, General Manager
Masayuki Tomita, Deputy General Managerr

Amari John (from 2020/4/27)
Motoko Kakubayashi
Marina Komori
Aya Tsuboi

Kavli IPMU Annual Report 2020

Accounting
Shigeru Kobayashi*
Naoko Ishida
Hiromi Yoshida
Yukiko Yoshikawa

Kamioka Branch
Fumitoshi Sakai*
Masako Ishikura
Yoshimi Kakioka
Hitoshi Nakagawa(*section head)

Budget Control
Daisuke Hamada*
Madoka Okamoto
Tomoko Shiga
Kaori Watanabe

Staff

Contract & General Purchasing
Kenji Irie*
Yuri Kazama (from 2021/3/1)
Yoshiya Ohtaka (till 2021/2/15)
Takako Okawa
Sachiko Shimada
Tomoko Yamanaka

General Management
Manabu Hirano* (from 2020/10/1)
Kazumi Ichimura* (till 2020/9/30)
Yuuko Enomoto
Mika Miura
Ayako Nakada
Mana Shindo (from 2020/7/1)
Rieko Tamura

International Relations and Researchers Support
Yuko Fukuda* (from 2020/10/1)
Toshiko Furukawa* (till 2020/9/30)
Rie Kohama
Masami Nishikawa
Hinaka Ochiai
Eri Shinoda

Network and Web Service
Satoko Inoshita
Masahiro Kawada (from 2020/10/1)

Planning & Assessment
Shoko Ichikawa

Kavli IPMU Annual Report 202025

5.1 Gopakumar-Vafa Type Invariants on CalabiYau 4-Folds
Cao Yalong

Gromov-Witten (GW) invariants are rational numbers (virtually) counting stable maps from curves to symplectic manifolds.
They are not necessarily integers because of the possible multiple cover of a curve to itself. To figure out the underlying
integer-valued curve counting invariants is a fundamental question in the world of enumerative geometry. On symplectic
4-manifolds, this question is explored by C. Taubes using hard analytic tools in a series of groundbreaking works [1, 2],
where Seiberg- Witten invariants are deeply involved. Taubes’works are fundamentally important for our understanding of
symplectic 4-manifolds.
On Calabi-Yau 3-folds, this question resists to be attacked until the great insight from string theory comes by the work of R.
Gopakumar and C. Vafa [3]. Gopakumar and Vafa conjecture that there are integer-valued invariants (called GV invariants)
which contain equivalent information of GW invariants and give an explicit formula for them. Mathematically one can read
off GV invariants from GW invariants but the integrality of GV invariants is quite a nontrivial statement recently proved by E.
Ionel and T. Parker [4].

References[1]	C. H. Taubes, Counting pseudo-holomorphic submanifolds in dimension 4. J. Differential Geom. 44 (1996), no. 4, 818–
893[2]	C. H. Taubes, SW ⇒ Gr: from the Seiberg-Witten equations to pseudo-holomorphic curves, J. Amer. Math. Soc. 9 (1996),
no. 3, 845–918[3] R. Gopakumar and C. Vafa, M-theory and topological strings II, hep-th/9812127[4] E. N. Ionel and T. Parker, The Gopakumar-Vafa formula for symplectic manifolds, Ann. of Math. (2) 187 (2018), no. 1, 1–64
[5]	A. Klemm and R. Pandharipande, Enumerative geometry of Calabi-Yau 4-folds, Comm. Math. Phys. 281 (2008), 621–653[6]	S. K. Donaldson and R. P. Thomas, Gauge theory in higher dimensions in The Geometric Universe (Oxford, 1996), Oxford
Univ. Press, Oxford, 1998, 31–47[7]	S. Hosono, M. Saito and A. Takahashi, Relative Lefschetz actions and BPS state counting, Internat. Math. Res. Notices 15(2001), 783–816.
[8] S. Katz, Genus zero Gopakumar-Vafa invariants of contractible curves, J. Differential. Geom. 79 (2008), 185–195[9] D. Maulik and Y. Toda, Gopakumar-Vafa invariants via vanishing cycles, Invent. Math. 213 (2018), no. 3, 1017–1097[10]	Y. Cao, D. Maulik and Y. Toda, Genus zero Gopakumar-Vafa type invariants for Calabi-Yau 4-folds, Adv. Math. 338 (2018)
41–92.
[11]	Y. Cao, D. Maulik and Y. Toda, Stable pairs and Gopakumar-Vafa type invariants for Calabi-Yau 4-folds, J. Eur. Math. Soc.
(JEMS) 10.4171/JEMS/1110[12]	Y. Cao and Y. Toda, Gopakumar-Vafa type invariants on Calabi-Yau 4-folds via descendent insertions, Comm. Math. Phys.
383 (2021), no. 1, 281–310

On Calabi-Yau 4-folds, there seems no string theory insight into similar question. One major difference with CY 3-fold caseis that only genus 0 and 1 GW invariants are nontrivial on CY 4-folds by a Riemann- Roch calculation. One instead considersan ‘ideal’ situation where curves behave in expected ways to be able to compute everything explicitly. In [5], A. Klemm and
R. Pandharipande propose a definition of GV type invariants on CY 4-folds along this way. They conjecture the integralityof their invariants and do checks in lots of examples.

Research Highlights

5

RESEARCH HIGHLIGHTS

Research Highlights

Looking back to Taubes’works, one may wonder whether there are analogous gauge theoretic in- variants appearing in thecases of CY 3-folds and 4-folds. In [6], S. Donaldson and R. Thomas give a proposal to extend theories of A. Floer and S.
Donaldson on dimensions 3 and 4. However in com- plex dimensions 3 and 4, analytic tools are extremely difficult to workout, algebro-geometric method is necessary instead. In the setting of algebraic geometry, connections on bundles are
replaced by general coherent sheaves and differential equations are replaced by deformation-obstruction theory. In [7], S.
Hosono, M. Saito and A, Takahashi (see also S. Katz [8]) propose how to recover genus 0 GV invariants on CY 3-folds fromcounting invariants of stable sheaves which are supported on curves. Recently, such proposal is generalized to arbitrary
genus by D. Maulik and Y. Toda [9].
Then it is natural to ask whether there are parallel sheaf theoretic approaches to GV type invariants on CY 4-folds. In a series
of works [10, 11, 12], Yalong Cao, Yukinobu Toda at Kavli IPMU and Davesh Maulik at MIT give answers to this question. We
consider moduli spaces of one dimensional stable sheaves (or stable pairs) on CY 4-folds and integrations of insertions on
their virtual classes. Contrary to CY 3-fold case, our virtual dimension is positive, so invariants we define depend on the
choice of insertions (i.e. observables in physicists’ language). The most canonical insertion is given by the slant product ofChern characters of universal one dimensional sheaf by cohomology classes on the CY 4-fold. Insertions defined using thefirst nontrivial Chern character are called primary insertions and others are called descendent insertions. Our conjecture isthat primary counting invariants give genus 0 GV type invariants of Klemm-Pandharipande while descendent counting
invariants contain all genus 1 information. We prove our conjecture when CY 4-folds are ‘ideal’ and provide several computational evidences in examples. By a dimensional reduction, our genus 0 conjecture recovers the conjecture of HosonoSaito-Takahashi and Katz on CY 3-folds. The formulation of our genus 1 conjecture involves nontrivial constrains on genus
0 GW/GV invariants of CY 4-folds which we prove to be equivalent to the Witten-Dijkgraaf-Verlinde-Verlinde (WDVV) equations. It is an interesting question to give a physical interpretation of our works.

26

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202027

Research Highlights

5.2 (Co-) Evolution of Supermassive Black Holes
and Their Host Galaxies
John Silverman
Supermassive black holes (SMBHs) play an integral role in galaxy evolution. A coupling of their energy output to the surrounding gas internal to galaxies has been recognized as a vital ingredient for simulations to match the observed local mass
distribution of galaxies [1]. Such feedback effects occur during phases of mass accretion onto SMBHs, typically observed asquasars and Active Galactic Nuclei.
Hence, much effort has been undertaken to establish a direct causal connection between the growth of galaxies and their
SMBHs. In the local Universe, remarkable evidence exists for their coupled growth as seen by the tight relation between themass of SMBHs and the properties of their host galaxy (i.e., mass, velocity dispersion) as established by the Hubble Space
Telescope [2].
The central question is how the local mass relation got established, either black holes and their host galaxies grew together
in lock step (i.e., co-evolved) or one preceded the other where a Universe first seeded by black holes would open many newquestions. To determine how SMBHs and their host galaxies migrate onto the local mass relation, observations at earlier
cosmic times are needed to view the progenitors of such local systems.

Furthermore, the level of intrinsic scatter in the mass ratio (MBH/M*) at high redshift is low and matches the local value. Thisis surprising since one would expect the dispersion to increase with lookback time if the growth of galaxies and their black
holes is driven by primarily by galaxy mergers in a scenario of hierarchical assembly of structure. The current explanation isthat there is a physical coupling between SMBHs and their hosts through quasar feedback. This is supported by a comparison of the HST data to hydrodynamic simulations which include such feedback effects [5]. To add further intrigue, theseprocesses appear to be linked to galaxies undergoing structural changes from being disk- to bulge-dominated [6] asrequired to have SMBHs and their hosts migrate onto the local mass relation.
Currently, the wide-field optical imaging from the Hyper Suprime-Cam (HSC) Subaru Strategic Program is being used tosignificantly expand upon studies of the connection between SMBHs and their host galaxies up to z ~ 1 by using 5000
quasars from the Sloan Digital Sky Survey (SDSS) thus improving upon the statistical significance of the results.

Research Highlights

John Silverman, Xuheng Ding and their collaborators have completed an effort to establish the link between the mass of
SMBHs and the stellar mass of their host galaxies in the distant universe. To do so, the team has carried out a Hubble Space
Telescope (HST; PI Silverman) program based on near-infrared imaging with WFC3 of the host galaxies of 32 activelygrowing SMBHs at epochs when the Universe was only 4 billion years old (z ~ 1.5). Using sophisticated 2D image analysis
routines, they decompose the host galaxy emission from the bright quasar to measure their stellar mass (Figure 1 top).
Using black hole mass estimates from near-infrared spectroscopy with Subaru/FMOS [3], they find a ratio between the massof SMBHs and the stellar mass of their host galaxy consistent with the local relation thus indicating a co-evolutionary scenario (Figure 1 bottom; [4]) after proper selection biases are accounted for.

Figure 1: (Top) Example of 2D decomposition of an HST infrared image of an accreting SMBH with the hostgalaxy shown as “data - point source”. (Bottom) Mass ratio (MBH/M*) between SMBHs and their hostgalaxies relative to the local (z = 0) relation. The 32 accreting SMBHs at 1.2 < z < 1.7, observed by HST
to determine the mass in stars of their host galaxy, are shown in orange. Most of the increase in themass ratio relative to the local relation (horizontal line at y = 0) is due to a bias in the selection of thesample as indicated by the small purple circle. Therefore, the observations at high redshift are nearlyconsistent with the local ratio thus illustrative of a co-evolutionary scenario between SMBHs and their hostgalaxies.

References[1] Somerville, R., Dave, R., “Physical Models of Galaxy Formation in a Cosmological Framework”, 2015, ARA&A, 53, 51[2] Kormendy, J. Ho, L. C., “Coevolution (Or Not) of Supermassive Black Holes and Host Galaxies”, 2013, Annu. Rev. Astron.
Astr. 51, 511–653[3] Schulze, A., Silverman, J. D. et al., “An FMOS Survey of Moderate-luminosity, Broad-line AGNs in COSMOS, SXDS, and
E-CDF-S”, 2018, ApJS, 239, 22[4] Ding, X., Silverman, J. D., Tommaso, T. et al.,“The Mass Relations between Supermassive Black Holes and Their Host Galaxies at 1 < z < 2 HST-WFC3”, 2020, ApJ, 888, 1[5] Ding, X., Treu, T., Silverman, J. D. et al., ”Testing the Fidelity of Simulations of Black Hole-Galaxy Coevolution at z ∼ 1.5 with
Observations”, 2020, ApJ, 896, 159[6] Silverman, J. D., Ding, X. et al.“Where Do Quasar Hosts Lie with Respect to the Size–Mass Relation of Galaxies?“, 2019, ApJ,
887, L5

28

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202029

Research Highlights

Kai Martens
Dark Matter (DM) is out there. That much we know from our ever growing knowledge and understanding of the Universe
we live in. As we integrated our knowledge of the particles that make up ordinary matter with careful observations of theluminous wonders dotting a clear, dark night-sky, we arrived at a consistent story of how our Universe evolved. And DM is
an indispensable ingredient to and actor in this story.
But this was also a bit of a humbling experience: Our trusty “standard model” (SM) of particle physics has no candidate for a
DM particle with the properties astronomical observations require of it: we really do not know what DM is. Astronomical
observations tell us that our planet and its Sun are plowing through our Milky Way’s halo of DM particles. If there is any kindof interaction with these DM particles other than the gravitational one, we should be able to see collisions mediated by thatinteraction between the DM halo particles and ordinary matter particles in a suitably designed detector here on Earth. Thatis the idea of a direct detection experiment. Liquid xenon (LXe) experiments are currently the most sensitive such experiments for DM particles with masses on GeV to TeV scales. The XENON collaboration LXe experiments look for signs of DM
particles’ collisions with ordinary matter as the Earth moves through the Milky Way’s DM halo.
Watching DM all throughout the Universe allows us to constrain what a collision between individual DM particles andparticles of ordinary matter should look like. First and foremost it informs us that such a collision must be very, very weak.
It also tells us that DM particles themselves should be moving slow enough that indeed the motion of our Earth throughthis DM particle halo is relevant for such collisions. To detect DM particles – and thus get a handle to study their true nature– we therefore need to build detectors that are:• very massive, so that our detector’s target material contains as many electrons and nuclei as possible for the DM particles to collide with• very clean in terms of the detector’s own radioactivity, so that radioactive decays in and around the detector cannot
overwhelm recoils from collisions with DM particles• hidden as far underground as is practical, so that penetrating remnants of cosmic rays cannot produce new radioactive isotopes in the detector material itself
The most important choice in designing a DM particle detector is that of the detector’s target material: the material in which
either electron (ER) or nuclear (NR) recoils from collisions with DM particles or radioactive decays will be recorded. Most of
the time it is impossible to know if the detector saw a radioactive decay or a collision with a DM particle; that means we needto find target and detector materials that contain as few radioactive isotopes as possible.

1. purification in the liquid phase of xenon to remove electronegative contaminants
2. a water Cherenkov based neutron veto surrounding the LXe target’s cryostat
222
3. radon distillation to reduce the equilibrium Rn concentration in the LXe target
The point here is that with the larger overall exposure each new generation of LXe experiments is collecting, previously
acceptable background now has to be suppressed. Kavli IPMU played a particularly important role in designing the neutron veto for XENONnT. Figure 2 shows the new, white neutron veto volume inside the existing gray muon veto water
shield. Inside the octagonal neutron veto is the cylindrical LXe target, also clad in white for optimal efficiency of the neutron
veto. Both, the outer muon veto and the inner neutron veto, will use the same gadolinium loaded water, allowing for highefficiency tagging of neutrons as soon as they emerge from the detector’s LXe target and get captured on Gd. The new
Gd-water system that maintains water transparency in the veto counters uses technology originally proposed for use at
Super-Kamiokande (SK) by KIPMU’s Prof. Mark Vagins. The XENONnT Gd-water system also incorporates some newer
developments made for SK at the Kamioka Observatory, which now allow SK to tag inverse beta decays throughout its
whole inner detector volume. This is a great example for synergy between the different experimental programs at Kavli
IPMU’s Kamioka Branch. Another important Japanese contribution was to the liquid phase purification of the detector’s
LXe target material.
At the time of writing this article XENONnT is taking first science data. The most immediate goal for XENONnT is to follow
up on XENON1T’s much discussed excess of low energy electron recoil events: With our new, enlarged, and cleaner LXetarget and the new, larger structures providing the drift field and holding more photomultipliers, the background situationis very different from XENON1T. If the excess is reproduced in XENONnT, the higher statistic and changed environment will
ultimately allow us to determine its true origin.
After ~5 years of data taking with XENONnT we hope to have observed first DM particle interactions in the detector – if not,–48
2
we will push the exclusion limit for a 50 GeV weakly interacting massive particle down to 1.4 × 10 cm . What else will weeither discover or learn? Our data will show, and our analysis methods are designed to prevent errors.
rdnd

The next, 3 generation of LXe drift chambers after the current ~10 ton 2 generation will require ~50 tons of xenon, toomuch for the world to afford more than one detector. The PIs and senior members of DARWIN/XENON – among themmyself – and LUX-ZEPLIN (LZ) have recently signed a Memorandum of Understanding and pledged to work together tobuild that 3rd generation detector, combining our respective strengths to deliver to the world the optimal detector in thisnext, presumably final, round of LXe DM hunting, which will push our detection capability to where neutrinos become themajor background.

Research Highlights

5.3 XENONnT – Finding Dark Matter Particles
with Liquid Xenon

After the successful conclusion of the XMASS experiment at the Kamioka Observatory here in Japan three of the XMASS
groups joined the XENON collaboration at the end of 2017 to help upgrade the XENON1T detector to XENONnT. Figure 1
shows the infrastructure supporting the detector in Hall B underground at the Laboratori Nazionali del Gran Sasso (LNGS)
in Italy. Apart from the 3-fold increase in LXe target mass the upgrade also introduced three new detector sub-systems,
each targeting a specific background contribution or signal loss mechanism to maximize the cumulative sensitivity of theexperiment:

Liquid xenon (LXe) is the target material of choice in today’s highest sensitivity DM particle detectors. It has dominateddirect detection DM searches since in 2008 XENON10 for the first time produced limits that reached beyond those obtainedwith other materials. Noble gases in general are attractive target materials because their chemical inertness allows for
efficient cleaning from contaminants that are not themselves noble gases, while distillation allows to also separate out
traces of other noble gases. And simply filling liquid in a bigger bucket allows for easy scaling of target mass. Xenon is theheaviest of the noble gases, and unlike argon it has no radioactive isotope with a half-life that would make it a source of
background intrinsic to the detector’s target mass. The half-life of the neutrinoless double beta (0νββ) decay candidate 136Xe
on the other hand is long enough that its background contribution remains acceptable while its presence adds new physics potential to the detector – the search for 0νββ-decay is still on-going. Another advantage of LXe targets is their highdensity, which provides effective shielding against external gamma radiation.
Right now three very similar LXe detectors are competing or getting ready to compete to be the first to find DM particles:
XENONnT, LZ, and PandaX-4T. All use dual-phase LXe detectors drifting electrons to independently measure both, thedirect scintillation light yield and the ionization yield from a charged particle recoiling in the detector. The relative strengthof these two signals allows efficient discrimination between nuclear and electron recoils and thus provide a powerfulmeans to isolate nuclear recoil signals in the presence of the ubiquitous electron recoil background from residual radioactive contamination. Since 2008 this detector design has consistently lead the field – and is still doing so.

30

Kavli IPMU Annual Report 2020

Figure 1: XENONnT support building and structures in Hall B at LNGS

Figure 2: White neutron veto surrounding the LXe target

Kavli IPMU Annual Report 202031

Research Highlights

5.4 Guided by EGADS, Loading SuperKamiokande with Gadolinium for the FirstTimeMark Vagins

In order to conclusively demonstrate that the GADZOOKS! concept was viable, in 2009 a new experimental chamber was
excavated in the Kamioka mine, close to Super–K. There, a dedicated, large-scale gadolinium test facility and water Cherenkov detector (a 200-ton scale model of Super–K), was built as depicted in Figure 1. Known as EGADS (Evaluating Gadolinium’s Action on Detector Systems), this joint ICRR/IPMU project was designed to make absolutely sure that the introductionof Gd would allow neutrons to be seen without impairing the water quality or adversely affecting the detector materials.
After years of work, the EGADS studies ultimately showed that putting gadolinium in Super-K should work exactly as predicted [2]. As a result, the SK tank was drained and refurbished in 2018/9 in preparation for the loading of gadolinium.

th

Finally, on July 14 , 2020, the first gadolinium sulfate was dissolved and injected into the SK tank. As shown in Figure 2, theprocedure involved laboriously transporting the gadolinium sulfate in small buckets which were then emptied into thedissolving system’s hopper. Working round-the-clock in this manner, Gd-loaded water was continuously injected until, on
August 17th, 2020, a total of 13.2 tons of Gd2(SO4)3 had been transferred into the SK water. This brought the concentration bymass of dissolved Gd3+ ions to 0.01%, meaning that - as shown in Figure 3 - about 50% of the neutrons in SK were being
captured on gadolinium (the remainder mostly wind up invisibly on hydrogen just as before) and could now be seen. A
tagged neutron-emitting calibration source was deployed at various positions in the SK tank and confirmed both the fraction of visible neutron captures as well as the uniformity of gadolinium loading within the detector.
Everything has been working as expected in SK at 0.01% Gd3+, but even higher neutron capture efficiency is desired. So, in
November of 2020 the Gd loading of EGADS was increased to 0.03% Gd3+ ions bring its visible neutron fraction to about
75%. Again, all went well with this demonstration, and so the plan to similarly increase Super-K’s loading to 0.03% in 2022
was officially approved. As this is a flagship Kavli IPMU experimental initiative, the Institute has agreed to help purchase SK’s
additional 27 tons of Gd2(SO4)3.
It has certainly been a long journey, but exciting new SK data are already being collected!

Research Highlights

Nearly two decades ago, Ohio State University theorist John Beacom and Kavli IPMU Professor and PI Mark Vagins first
proposed introducing tons of a water-soluble gadolinium [Gd] compound, gadolinium chloride, GdCl3, or the less reactive
though also less soluble gadolinium sulfate, Gd2(SO4)3, into the Super–Kamiokande (Super-K, SK) detector. Originally calledGADZOOKS! (Gadolinium Antineutrino Detector Zealously Outperforming Old Kamiokande, Super!), this load-SK-with-Gdidea was then detailed in a Physical Review Letters article [1]. Dissolving Gd in SK means that neutrons, nearly invisible in purewater Cherenkov detectors, would be rapidly captured on the aqueous Gd ions, leaving their nuclei in a highly-excited state
which would then decay, emitting bursts of easily detectable gamma rays. Making neutrons visible and thereby gaining
hitherto unattainable end-state information from particle interactions would allow a very large reduction, about a factor of
104, in Super-K’s physics background rates and greatly enhance the detector’s response to both supernova neutrinos (galactic and diffuse) and reactor antineutrinos. Many other physics topics would also benefit, from proton decay searches tostudies of atmospheric, solar, and long-baseline neutrino oscillations.

Figure 2: Carrying pure gadolinium sulfate to be dissolved andinjected into Super-K.

Figure 1: EGADS, the large-scale gadolinium test facility in the Kamioka mine

32

Kavli IPMU Annual Report 2020

Figure 3: The relationship between Gd concentration in the water and visible neutron
capture.

References[1] J. F. Beacom and M. R. Vagins,“GADZOOKS! Anti-neutrino spectroscopy with large water Cherenkov detectors,”Phys. Rev.
Lett. 93, 171101 (2004) [hep-ph/0309300][2] Ll. Marti et al., “Evaluation of gadolinium’s action on water Cherenkov detector systems with EGADS,” Nucl.Instrum.
Meth.A 959 (2020) 163549 [arXiv:1908.11532 [physics.ins-det]]

Kavli IPMU Annual Report 202033

Research Highlights

5.5 Subaru Prime Focus Spectrograph (PFS):
Towards Science Operation
Masahiro Takada
Thus the PFS instrumentation is relatively well underway even during this COVID-19 period. The PFS team is planning tohave the first “real”on-sky observation with the PFS PFI, fiber cable and spectrograph module in the commissioning runs ofOctober and November 2021. This will be a big milestone for the PFS project, and we look forward to these commissioningdata.

Research Highlights

We at Kavli IPMU are working on a major astronomical instrument project, called PFS (Prime Focus Spectrograph), which
has been promoted by the international collaboration that involves various institutes: Kavli IPMU, National Astronomical
Observatory of Japan (NAOJ), Academic Sinica Institute of Astronomy and Astrophysics (ASIAA) in Taiwan, California Institute of Technology (Caltech)/NASA Jet Propulsion Laboratory, Princeton University, Johns Hopkins University, Brazilian
Consortium, Group of Max Planck Society in Germany, Chinese PFS Participation Consortium (CPPC), and North-East Participation Group (NEPG) in the US. PFS is a next generation facility instrument on the 8.2 m Subaru Telescope at the 4,200 m
summit of Mt. Maunakea in Hawaii. It is a very wide-field, massively-multiplexed, and optical & near-infrared spectrograph,
and Kavli IPMU is the leading institute in both aspects of the instrument development and the planning of a 360-nightobservation campaign for three major science areas of cosmology, galaxy evolution, and Galactic archaeology. Exploiting
the Subaru’s prime focus, 2394 reconfigurable fibers will be distributed in the 1.3 degree-diameter field of view. The spectrograph system has been designed with 3 arms of blue, red, and near-infrared cameras to simultaneously deliver spectrafrom 380 nm to 1260 nm in one exposure. From the Subaru’s prime focus, the Hyper Suprime-Cam (HSC) has been continuously delivering superb imaging data over a large area of the sky. Conducting spectroscopic follow-up of HSC objects(stars and galaxies) with PFS is crucial to complete a comprehensive census of the universe. This is unique not only because
it exploits the unique capabilities of the Subaru Telescope such as the light-gathering power of the 8.2 m primary mirror,
and the wide field of view on the prime focus, but also because HSC and PFS enable deep imaging and spectroscopic surveys of the same patches of the sky using the same telescope and from the same site, so one can well understand various
systematics in the data which is essential for robust understandings of statistical properties of the universe.
The instrumentation has been carried out by the above international collaboration, being managed by the PFS Project
Office: Project Manager is a Kavli IPMU member, Naoyuki Tamura. During this difficult period of 2020 and 2021 under the
COVID-19 pandemic, the Project Office has made best efforts to minimize the impact on the instrumentation. The team is
actively integrating and testing the hardware and software of the subsystems, and some of them have been delivered to
the Subaru Telescope observatory. In September 2020 the team successfully installed all about 2400“Cobra”positioners on
the focal plane of the Prime Focus Instrument (PFI) at ASIAA in Taiwan (Fig. 1). The Cobra positioner, which was mainly
developed at Caltech/JPL, is a slender, two-stage motor assembly system that is capable of positioning a fiber to a desired
target to within of 5 micrometer. The PFI was successfully shipped to and arrived at the Subaru Telescope in Hawaii in June
2021, and is now being tested at the telescope site (Fig. 1). One of major challenges for an observation with PFS is a precise
calibration of the night sky emission. To tackle this problem, the team had a big milestone during 2021. The team installeda pair of small-aperture (36 mm) telescopes, named the Subaru Night Sky Spectrograph (SuNSS), on the top ring of the
Subaru Telescope in February 2021. Both SuNSS telescopes have the same focal ratio and the same field of view as PFS, andcan receive the same sky signal through the fiber as that of the PFI and can deliver the sky light to PFS fiber cable unit andthen to PFS spectrograph modules. As shown in Fig. 2, the team successfully obtained the sky spectra as well as spectra ofstars with the SuNSS and the PFS spectrograph. The spectra were used to test and refine the PFS data analysis pipeline.

Figure 2 (Upper-left panel): A photo of the Subaru Night Sky Spectrograph (SuNSS) system. The image (a) is a photo of the
SuNSS system, the image (b) is the two SuNSS telescopes (each of which has 36 mm aperture), and (c) is the fiber
cable unit. The SuNSS was installed on the top ring of the Subaru Telescope, as indicated by the upper-rightimage, in February 2021. (Lower four panels): The night sky spectra taken with SuNSS that delivers the sky light to
the PFS fiber cable unit and PFS spectrograph module. The bottom two panels show the sky spectra that are
obtained by the PFS data analysis pipeline. The vertical lines in the bottom right panel denotes the expected
wavelengths of OH sky lines, in the wavelength range from 870 to 915 nanometers.

Figure 1 (Left panel): A photo of the PFS Prime Focus Instrument (PFI), taken at the Academic Sinica Institute of Astronomy and Astrophysics (ASIAA) in
Taiwan. All about 2400 “cobra”positioners were installed in PFI in September 2020. (Right panel): A photo of PFI taken at the Subaru Telescope.
PFI was successfully shipped to the Subaru Telescope in Hawaii in June 2021.

34

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202035

Research Highlights
In parallel to the PFS instrumentation, the PFS Science Working Group is developing a timely, concrete plan of large-sky
survey observation to be proposed and conducted in the framework of Subaru Strategic Program (SSP). Having the threemain survey components in areas of cosmology, galaxy evolution, and Galactic archaeology, the team is aiming at addressing key questions in the modern cosmology and astrophysics by multiple approaches over multiple scales of dark matter
density structure, leading to comprehensive challenges to the ΛCDM structure formation paradigm (see the lower panel ofFig. 3). During the COVID-19 period, the team has been continuously updating and refining the plan in detail through discussions regularly by remote meetings and e-mails (Fig. 3). The team, being led by the Science WG co-chairs Masahiro
Takada (Kavli IPMU) and Richard Ellis (UCL), completed the writing of the draft of the PFS SSP proposal that will be submitted
to the Subaru community in 2022. The proposal is now being reviewed by the external review committee members,
assigned by the FPS team, that consist of world-leading experts in cosmology and survey astronomy. We envision that wewill start our science operation in 2023. As we are approaching the period of on-sky engineering observations and start of
the PFS SSP survey, the interplays between the science team and technical team are more and more crucial, to share not
only the basic performances but also the other detailed characteristics of the instrument, and mutually optimize the software components, data flow, and survey management. The members in Kavli IPMU will be playing key roles not only in the
integration and commissioning of the PFS instrument, but also in the coagulation of the entire collaboration during thecoming key phases of the project in the following fiscal years for ultimate scientific and technical success of PFS.

5.6 Resolution of Singularities ofThermal Correlators in String Theory
Matthew Dodelson
The fundamental objects in conformal field theory are correlation functions, which measure the correlations between
operators at different points in spacetime. One interesting property of these correlation functions is the location of their
singularities. At zero temperature the correlation function is singular when two points are lightlike separated, corresponding to a massless particle propagating between the two points. In recent work with Oogur[1], we studied the analogous
question at finite temperature. In particular, we addressed possible singularities in the thermal two point function in theLorentzian regime.

Although the aforementioned analysis shows that the singularity arises in the strict holographic limit, it may be the case that
it is actually resolved at finite coupling constant, corresponding to a finite but small string length. We showed that thisresolution indeed occurs by studying string theory in the black hole background. This string theory can be solved exactly
by going to the Penrose limit, which describes the geometry very close to the null geodesic. Carrying out the analysis ofstringy excitations, one finds that tidal effects stretch out the string more and more as one goes closer and closer to thegeodesic. These tidal effects lead to production of massive particles on the worldsheet, which resolves the singularity on
the light cone. The behavior of the correlation function near the light cone therefore probes string theory in the bulk, leading to a novel interesting connection between string theory and conformal field theory.

Research Highlights

To study this question, we made use of the AdS/CFT duality, which relates conformal field theory in d dimensions to a
gravitational theory in d+1 dimensions. In this duality, a thermal state on the boundary is mapped to a black hole in Anti deSitter space. Singularities of the two-point function in the conformal field theory then correspond to null geodesics connecting two boundary points. Therefore the problem can be reduced to classifying all possible null geodesics in the blackhole background that extend to infinity. We showed that in addition to the standard light cone, there are new exotic singularities corresponding to null geodesics that extend into the bulk. These additional null geodesics may wrap the photon
sphere many times, and give new singularities in the thermal two point function in the holographic limit.

Reference[1] M. Dodelson and H. Ooguri, ”Singularities of thermal correlators at strong coupling,” Phys. Rev. D 103, 066018 (2021)
Figure 3 (Upper panel): A photo of the online 12th PFS collaboration meeting. (Lower panel): Top-level scientific goals we aim at achieving with theplanned PFS program spending 360 Subaru nights over 5 years from 2023.

36

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202037

Research Highlights

5.7 Perverse Sheaves and Their Categorification

5.8 Milky Way Dark Matter SeverelyConstrained by Two New Papers

Mikhail Kapranov

Oscar Macias

Perverse sheaves are local topological data, analogous to those expressed by the mathematical concept of a sheaf. They
were introduced in the 1980s in the study of singular algebraic varieties, to provide far-reaching generalizations of various
dualities in topology such as Poincaré duality between homology and cohomology. The name “perverse sheaves” simply
signifies that they are analogous to sheaves but are not sheaves. In fact, they appear naturally in many areas such as linear
PDE.
In many cases perverse sheaves can be classified by quiver diagrams such as
a

Ψ.

(1)

b

In this particular case (corresponding to perverse sheaves on the complex line with one singularity) Φ is known as the spaceof vanishing cycles and Ψ as the space of nearby cycles. Such diagrams tend to be of balanced nature (arrows going back andforth) which matches the self-dual nature of perverse sheaves themselves. Another example of such balanced structure isprovided by the concept of a Hopf algebra so important both in algebra and in mathematical physics (quantum groups). A
Hopf algebra A, although not a quiver diagram, has both a multiplication and a comultiplication going in opposite directions
AA

mult.

A,

A

comult.

A  A.

In fact, one can relate Hopf algebras with perverse sheaves on the configuration spaces, which are the space of polynomials
in one variable
f(x) = xn + a1xn−1 + · · · + an,

A strong glow of either WIMPs or Axion emission is expected to be originated in the center of the Milky Way. This is bothbecause of its proximity to Earth, and the very large concentration of Dark Matter particles in that sky region. However, thecharacteristics of the emission from either candidate are predicted to be very different. In the case of WIMPs, since suchparticles have masses that are a few hundred times heavier than that of a proton, the glow of their self-destruction (ordecay) could be observable with highly energetic light detectors (gamma-ray telescopes). While in the case of Axions,which have masses smaller than a billionth times the mass of an electron, their emission could be measured with telescopes
scanning the sky for less energetic light signals (radio telescopes).
In two separate articles [1, 2], we have searched for emission of WIMP and Axion Dark Matter in data collected by the Fermi
Gamma-Rays Space Telescope, and the Effelsberg Radio Telescope, respectively. We have meticulously modeled the astrophysical background (regular emission from objects such as stellar objects, interstellar gas, etc.) in the Galactic Center andconcluded that up to the sensitivity level of these instruments, the observations are consistent with the background-only
hypothesis. This is the same to say that if either WIMPs or Axions turned out be correct descriptions of Dark Matter, theyshould be emitting signals that are below the limits displayed in Fig.1.

stratified by the multiplicity of roots. See [1, 2].
An important organizing principle in mathematics is that of categorification, i.e., lifting numerical data to data consisting ofvector spaces and the latter to data consisting of cate- gories. In this way, for example, the scalar product (a number) (a, b)of vectors in a Hilbert space can be sometimes upgraded to the vector space of morphisms Hom (A, B) in a category. It was
proposed sometime ago by M. Kapranov and V. Schechtman that the concept of a perverse sheaf itself should allow sucha categorfied lifting; these conjectural structures were called perverse schobers.
One can give a precise meaning to perverse schobers in one dimension, and the resulting theory is already very interesting.
For example, the study of Fourier transform of perverse schobers, very natural from the point of view of analogy with PDE,
leads to a natural conceptual explanation of the Algebra of the Infrared of Gaiotto-Moore-Witten, a certain “calculus ofconvex polygons” [3]. See [4] This suggests that a natural encoding of the infrared behavior of a certain class of supersymmetric 2d quantum fi theories can be provided by a perverse schober on the complex plane of central charges. The singularities are the central charges of various vacua of the theory. The “vanishing cycles categories”, i.e., the categorical analogsof the spaces Φ in (1), are the categories of D-branes corresponding to the vacua, and the tunnelling between the vacua is
encoded by the perverse schober structure.

Research Highlights

Φ

The Universe is filled with an invisible substance (called “Dark Matter”) that holds galaxies and clusters of galaxies together.
While we are certain of its existence, it is still unclear what are its ingredients. Many particle physics models predict newparticles with just the right properties to explain away the astrophysical observations of Dark Matter. Two of the mostpopular Dark Matter particle candidates are: WIMPs (Weakly Interacting Massive Particles) and Axions. The former is implicated in solving the so-called “hierarchy problem” —which is associated with explaining the large hierarchy between the electroweak and the Plank scale— and the latter is involved in preventing the model from assigning a particle in the nucleus ofevery atom (the neutron); properties that are inconsistent with laboratory observations.

ts

imi

ark

D
GC

M

er l
att

Fig.1. Left: The limits on Axion coupling with photons as a function of the axion mass (black lines). Previous limits from the CAST helioscope and the UF and RBF
haloscopes are shown in shaded grey. The range of couplings expected for the QCD axion is shaded in orange. The green band depicts theoretical uncertainties on the Axion coupling limit associated with the GC analysis for the Eﬀelsberg data. Right: The limits on the average dark matter cross section times relative

References[1] M. Kapranov, V. Schechtman. Shuﬄ algebras and perverse sheaves. arxiv:1904.09325.
[2] M. Kapranov, V. Schechtman. PROBs and perverse sheaves I. Symmetric products. arXiv:2102.13321.
[3] D. Gaiotto, G. W. Moore, E. Witten. Algebra of the Infrared: String Field Theoretic Structures in Massive N=(2,2) Field
Theory In Two Dimensions. arXiv:1506.04087.
[4] M. Kapranov, Y. Soibelman, L. Soukhanov. Perverse schobers and the Algebra of the Infrared. arXiv:2011.00845.

velocity for WIMP particles self-destructing in bottom quarks. The parameter space above the red line is ruled out by null observations of WIMPs from the
Galactic Center. Previous limits from dwarf spheroidal galaxies are shown by a green curve. Current limits by the H.E.S.S. observatory are represented by the blacksolid line. The dashed line is the thermal Dark Matter cross section.

References[1] https://www.ipmu.jp/en/20200914-ThermalRelic-DM[2] https://www.ipmu.jp/en/20201218-AxionDarkMatter

38

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202039

Research Highlights

Shunichi Horigome
The Standard Model (SM) of particle physics is a well-established framework describing our world with high accuracy, but
it is not complete yet. Various cosmological and astrophysical observations show the presence of dark matter (DM), an
unknown source of the gravitational force in the universe. Since observations show that it is mainly difficult for macroscopic objects such as primordial black holes to account for all of the DM mass except for a small mass region, most physicists believe that DM is a kind of unknown particle not listed in the SM [1]. The study of DM could therefore lead to a
deeper understanding of particle physics.
Once we assume particle DM, from the viewpoint of quantum physics, DM can be categorized by its quantum numbers(charges) such as particle statistics (boson, fermion), the color charge of the strong interaction, the weak isospin, and theU(1) hypercharge. Different compositions of these quantum numbers describe different candidates of DM, hence we havevarious phenomenology of DM candidates. In particular, electroweakly interacting massive particle (EWIMP) is a well-motivated candidate because some theoretically-motivated extensions of the SM predict the presence of such new particles,
and also it can naturally explain the relic density of DM in the present universe by the so-called freeze-out mechanism.
Dark matter candidates can be detected by using several detection methods: pair creation detection, direct detection, andindirect detection. Each method has its own advantages and disadvantages and should be used appropriately in different
cases. In the case of EWIMP, the indirect detection method is useful because of the enhancement of the annihilation crosssection thanks to the non-relativistic quantum effect, Sommerfeld enhancement [2]. Actually, the gamma-ray observation
by Fermi Large Area Telescope (Fermi-LAT) excludes EWIMP DM whose cross-section is less than O(1026) cm3s−1 when assuming the DM mass is O(10 − 100) GeV.
The indirect detection method utilizes the annihilation of DM particles in astronomical objects in the universe. When DM
annihilates into known particles such as gamma-ray, we can detect these signals by telescopes. In order to increase theefficiency of the detection, target objects must contain as a large amount of DM as possible and their signal-noise ratio
must be small. With this taken into consideration, it is known that dwarf spheroidal galaxies (dSphs) are hopeful targets
satisfying both conditions.
However, the indirect detection utilizing dSphs suffers from two kinds of biases: i) Biases from dSph modeling and ii) thosefrom data contamination. The former one stems from the fact that we have not determined yet a proper model describing
actual dSph systems, hence there is ambiguity in the choice of empirical models. On the other hand, the latter one is dueto the contamination of non-dSph member stars when observing dSphs (see fig. 1). These biases could generate large(about O(10)) systematical uncertainty of the DM constraint, which is problematic in the current and future DM detection.

Research Highlights

5.9 Foreground Effect on the J-Factor
Estimation of Dwarf Spheroidal Galaxies

In our study [3, 4], we focused on the latter one, the foreground contamina- tion effect, and developed a new method thatcan estimate the amount of DM in dSphs even under the influence of the contamination effect. Generally, the amount of
DM is estimated by solving dSph kinematics with a spectroscopic stellar data set. In the conventional method, the stellar
data set is sorted by using the expectation-maximization (EM) algorithm. Non-member-like stars are eliminated before thekinematical analysis, and only the member-like stars are used in the estimation of the amount of DM. However, there aresome issues in this procedure; what we can observe by spectroscopic telescopes is just the velocity projected along theline-of-sight, hence it is difficult in principle to dis- tinguish whether some stars are members or non-members. The conventional method forces these ambiguous stars to be distinguished, which is a source of systematical bias. Moreover, theEM algorithm requires a too simplified approx- imation of the dSph distribution model (flat velocity dispersion profile),
which is also problematic. In order to solve these problems, our method models not only member stars but also nonmember stars based on a well-motivated stellar distribution model. All of the stars including ambiguous ones are thenanalyzed simultaneously, and the amount of DM is directly obtained. This method allows us to estimate the amount of DM
in a statistically proper way, in contrast with the conventional method, whose systematical bias cannot be estimated without additional analysis. Using our method, in Ref. [5], we estimated the amount of DM of some hopeful dSphs: Draco,
Sculptor, and Ursa Minor, reported as very DM-rich dSphs.
Figure 2 shows that the amount of DM estimated by using different methods. The DM amounts obtained by our method
are almost consistent with those reported in the conventional method but slightly deviated from each other due to thecontamination effect. We also emphasized that this difference must be larger in the case of ultrafaint dSphs, dSphs recently discovered thanks to improved detection capabilities of telescopes, because of the smaller number of member stars. Our
method is a powerful tool even for such a case and works better by using larger stellar data set collected by future spectroscopic telescopes such as Prime Focus Spectrograph (PFS) mounted on the Subaru telescope.

Figure 2: J -factor values (squared DM density averaged over the certain region in the celestial sphere) estimated by using
our method (black bars) and other conventional methods (colored bars).

Figure 1: Illustration of the foreground contamination. Blue and yellow stars denote member stars

References[1] Anne M. Green and Bradley J. Kavanagh. Primordial Black Holes as a dark matter candidate. J. Phys. G, 48(4):043001, 2021.
[2] Junji Hisano, Shigeki Matsumoto, and Mihoko M. Nojiri. Explosive dark matter annihilation. Phys. Rev. Lett., 92:031303,
2004.
[3] Koji Ichikawa, Miho N. Ishigaki, Shigeki Matsumoto, Masahiro Ibe, Hajime Sugai, Kohei Hayashi, and Shun-ichi Horigome.
Foreground effect on the J -factor estimation of classical dwarf spheroidal galaxies. Mon. Not. Roy. Astron. Soc., 468(3):2884–
2896, 2017.
[4] Koji Ichikawa, Shun-ichi Horigome, Miho N. Ishigaki, Shigeki Matsumoto, Masahiro Ibe, Hajime Sugai, and Kohei Hayashi.
Foreground effect on the J -factor estimation of ultrafaint dwarf spheroidal galaxies. Mon. Not. Roy. Astron. Soc., 479(1):64–
74, 2018.
[5] Shun-ichi Horigome, Kohei Hayashi, Masahiro Ibe, Miho N. Ishigaki, Shigeki Matsumoto, and Hajime Sugai. J -factor estimation of Draco, Sculptor and Ursa Minor dwarf spheroidal galaxies with the member/foreground mixture model. Mon.
Not. Roy. Astron. Soc., 499(3):3320–3337, 2020.

of a dSph and non-member stars (mainly from the Milky Way), respectively. It is difficult
for us to distinguish these stars only by using spectroscopic data set, because .

40

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202041

Research Highlights

5.10 Sign of Hard X-Ray Pulsation from theGamma-Ray Binary System LS 5039
Tadayuki Takahashi

Gamma-ray binaries are a subclass of binary systems consisting of massive stars and compact stars. They were discovered
only recently, in 2004, when observations of very-high-energy gamma-rays in the teraelectronvolt (TeV) band from large
enough regions of the sky became possible. When viewed with visible light, gamma-ray binaries appear as bright bluishwhite stars, and are indistinguishable from any other binary system hosting a massive star. However, when observed with
X-rays and gamma-rays, their properties are dramatically different from those of other binaries. In these energy bands,
ordinary binary systems are completely invisible, but gamma-ray binaries produce intense non-thermal emission, and theirintensity appears to increase and decrease according to their orbital periods of several days to several years.
Once the gamma-ray binaries were established as a new astrophysical class, it was quickly recognized that an extremely
efficient acceleration mechanism should operate in them. While the acceleration of TeV particles requires tens of years insupernova remnants, which are renowned cosmic accelerators, gamma-ray binaries boost electron energy beyond 1 TeV injust tens of seconds. Gamma-ray binaries can thus be considered one of the most efficient particle accelerators in the Universe.

Both observations, while separated by nine years, provided evidence of a neutron star at the core of LS 5039: the periodic
signal from Suzaku with a period of about 9 seconds. The probability that this signal arises from statistical fluctuations isonly 0.1 percent. NuSTAR also showed a very similar pulse signal, though the pulse significance was lower—the NuSTAR
data, for instance, was only tentative. By combining these results, it was also inferred that the spin period is increasing by
0.001 s every year.
Based on the derived spin period and the rate of its increase, the team ruled out the rotation-powered and accretionpowered scenarios, and found that the magnetic energy of the neutron star is the sole energy source that can power LS
115039. The required magnetic field reaches 10 T, which is 3 orders of magnitude higher than those of typical neutron stars.
This value is found among so-called magnetars, a subclass of neutron stars which have such an extremely strong magnetic
field. The pulse period of 9 seconds is typical of magnetars, and this strong magnetic field prevents the stellar wind of the
primary star from being captured by a neutron star, which can explain why LS 5039 does not exhibit properties similar to
X-ray pulsars (X-ray pulsars usually occur in X-ray binary systems, where the stellar winds are captured by its companionstar).
Interestingly, the 30 magnetars that have been found so far have all been found as isolated stars, so their existence ingamma-ray binaries was not considered a mainstream idea. Besides this new hypothesis, the team suggests a source thatpowers the non-thermal emission inside LS 5039—they propose that the emission is caused by an interaction between themagnetar’s magnetic fields and dense stellar winds. Indeed, their calculations suggest that gamma-rays with energies ofseveral MeVs, which has been unclear, can be strongly emitted if they are produced in a region of an extremely strong
magnetic field, close to a magnetar.

In addition, some gamma-ray binaries are known to emit strong gamma-rays with energies of several megaelectron volts(MeV). Gamma-rays in this band are currently difficult to observe; they were detected from only around 30 celestial bodies
in the whole sky. But the fact that such binaries emit strong radiation even in this energy band greatly adds to the mysterysurrounding them, and indicates an extremely effective particle acceleration process going on within them.

These results potentially settle the mystery as to the nature of the compact object within LS 5039, and the underlying
mechanism powering the binary system. However, further observations and refining of their research is needed to shed
new light on their findings.

Around 10 gamma-ray binaries have been found in the Galaxy thus far—compared to more than 300 X-ray binaries thatare known to exist. Why gamma-ray binaries are so rare is unknown, and, indeed, what the true nature of their acceleration
mechanism is, has been a mystery—until now.

Reference[1] H. Yoneda, K. Makishima, T. Enoto, D. Khangulyan, T. Matsumoto, T. Takahashi, “Sign of hard X-ray pulsation from the
gamma-ray binary system LS 5039”, Physical Review Letters 125 (2020) 111103

Research Highlights

A team including former graduate student Hiroki Yoneda, Senior Scientist Kazuo Makishima and Principal Investigator
Tadayuki Takahashi has analyzed previously collected data to infer the true nature of a compact object—found to be arotating magnetar, a type of neutron star with an extremely strong magnetic field—orbiting within LS 5039, the brightest
gamma-ray binary system in the Galaxy. They also suggest that the particle acceleration process known to occur within LS
5039 is caused by interactions between the dense stellar winds of its massive primary star, and ultra-strong magnetic fieldsof the rotating magnetar.

Through previous studies, it was already clear that a gamma-ray binary is generally made of a massive primary star thatweighs 20-30 times the mass of the Sun, and a companion star that must be a compact star, but it was not clear, in manycases, whether the compact star is a black hole or a neutron star. The research team started their attempt by figuring out
which is generally the case.
One of the most direct pieces of evidence for the presence of a neutron star is the detection of periodic fast pulsations,which are related to the neutron star rotation. Detection of such pulsation from a gamma-ray binary almost undoubtedly
discards the black hole scenario.
In this project, the team focused on LS 5039, which was discovered in 2005, and still keeps its position as the brightest
gamma-ray binary in the X-rays and gamma-ray range. Indeed, this gamma-ray binary was thought to contain a neutronstar because of its stable X-ray and TeV gamma-ray radiation. However, until now, attempts to detect such pulses had been
conducted with radio waves and soft X-rays—and because radio waves and soft X-rays are affected by the primary star’s
stellar winds, detection of such periodical pulses had not been successful.
This time, for the first time, the team focused on the hard X-ray band (>10 keV) and observation data from LS 5039 gatheredby the hard X-ray detector (HXD) on board the space-based telescopes Suzaku (between September 9 and 15, 2007) and
NuSTAR (between September 1 and 5, 2016)—indeed, the six-day Suzaku observation period was the longest yet using
hard X-rays.

42

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 202043

Research Highlights

Volodymyr Takhistov
Black holes (BHs), peculiar gravitational objects from which even light cannot escape, have been a central theme for bothscience as well as popular science media for decades. Definitively established to exist, BHs continue to harbor numerous
fascinating mysteries. As demonstrated in pioneering work by Deputy Director Misao Sasaki [1, 2], primordial black holes(PBHs) from the early Universe could be directly connected with the recent breakthrough gravitational wave (GW) observations by LIGO as well as the elusive dark matter (DM). Frontiers of PBH research are being advanced across variety of directions by leading scientists affiliated with IPMU including Masahiro Kawasaki, Kazunori Kohri, Alexander Kusenko, Masahiro
Takada and Tsutomu Yanagida.
Solar-mass BHs pose particular interest, as they are not expected from textbook astronomy and their detection could thus
promise discovery of new physics. Aside solar-mass PBHs, such BHs could also appear as “transmuted” [3] remnants ofneutron stars that were eventually swallowed by captured DM (either accumulation of particle DM or tiny PBHs). Intriguingly, solar-mass BH candidates have already been detected by LIGO. Where do they come from? As demonstrated in my
Physical Review Letters study [4], done in collaboration with George M. Fuller (UCSD) as well as Alexander Kusenko (UCLA/
Kavli IPMU), a simple but with powerful consequences idea is to analyze the detected BH mass distribution. As displayed inFig. 1 (left panel), transmuted BHs will follow the known neutron star mass distribution. This immediately leads to a striking> 1.5 M8 are unlikely to be from DM consuming neutron
result with significant implications for the DM, that BHs with mass ~stars. Statistical analyses exploiting this approach will further improve our understanding of DM with upcoming data.

5.12 Diversities of Supernovae and Their Origin
Ken’ichi Nomoto
Recent very extensive searches of supernovae (SNe) have led to discoveries of new types of supernovae. We (Ken Nomoto
and Shing-Chi Leung, a former Kavli IPMU Project Researcher until 2019 September, now a postdoc at Caltech) have studied
the following diverse topics of supernovae with international collaborators.
1. Type Ia Supernovae and Supernova Remnants
For Type Ia SNe, whether the progenitor is the Chandrasekhar mass (Chandra-mass) (~1.4M8) white dwarf (WD) or a subChandrasekhar (sub-Chandra) mass WD (~1.0–1.1M8) have long been controversial. Furthermore, the existence of a new
type of fainter Type Ia SNe has been established, which is now called Type Iax SNe. This has provided more controversial
materials. To identify the progenitors of SNe Ia (and Iax), is critically important for understanding the nature of dark energy
in cosmology and the origin of elements in the Universe.
We have taken the approach to examine the elemental abundances in the remnants of SNe Ia and compare them with thetheoretical models of SNe Ia. One of the keys to identify the progenitors is the abundance pattern of the ejecta observed in
the supernova remnants. There is one supernova remnant near the galactic center, Sgr A East, whose type has been
unknown and controversial. We have made a collaboration with a group in Amsterdam who analyzed the X-ray spectroscopic data taken by the Chandra X-ray observatory and obtained detailed elemental abundance pattern, especially ironpeak elements.
The results in Figure 1 shows that the Mn/Fe and Ni/Fe ratios are much higher than the solar abundance ratios. By comparing our theoretical models of various types of supernovae (types II, Ia, Iax), we found the observed abundance pattern is
uniquely explained by the abundance pattern of the pure deflagration model for SN Iax (Figure 1). The high Mn/Fe and Ni/
Fe ratios are realized in nucleosynthesis at central densities as high as 5×109 g cm−3. Such a high central density implies thatthe exploding star is the Chandra-mass WD. This is not the sub-Chandra WD where nuclear burning occurs at densities as
low as 106 g cm−3. In addition, the small S/Fe and Ca/Fe ratios indicate the Type Iax origin, which is the first evidence of theremnant of SNe Iax.

Research Highlights

5.11 Identifying the Origin of Black Holes

FIG. 1Significant attention has been devoted to PBH DM in the stellar and intermediate-mass ranges, prime for GW observations [1, 2]. As demonstrated in a series of works [5, 6] that I have led, which were carried out in collaboration with experts
from multiple areas of astronomy and high energy physics (including Alexander Kusenko, Yoshiyuki Inoue and Kohei
Hayashi affiliated with IPMU) and with results initially appearing in Astrophysical Journal Letters, such PBHs can leave significant imprints on host astrophysical systems due to their interaction with interstellar medium gas. Through variety ofmechanisms PBHs will deposit energy and heat onto the surrounding gas, which allows for a sensitive probe of PBH DM(especially in well understood systems, such as dwarf galaxy Leo T) over many orders of magnitude in mass, as shown in
Fig. 1 (right panel). Curiously, as demonstrated in a different study of mine [7], interactions and heating of surrounding gas
also allow to broadly explore emission from minute PBHs efficiently undergoing Hawking evaporation. Thus, gas heating
constitutes a novel powerful observable for probing PBHs independently of assumptions about cosmology.
The results of these studies help advance fundamental mission questions of Kavli IPMU, such as What is the Universe Madeof?, and allow us to understand the Nature from distinct perspectives at a deeper level.
References[1] T. Nakamura, M. Sasaki, T. Tanaka, and K. S. Thorne, Astrophys. J. Lett. 487, L139 (1997), arXiv:astro-ph/9708060 [astro-ph].
[2] M. Sasaki, T. Suyama, T. Tanaka, and S. Yokoyama, Phys. Rev. Lett. 117, 061101 (2016), arXiv:1603.08338 [astro-ph.CO].
[3] V. Takhistov, Phys. Lett. B782, 77 (2018), arXiv:1707.05849 [astro-ph.CO].
[4] V. Takhistov, G. M. Fuller, and A. Kusenko, Phys. Rev. Lett. 126, 071101 (2021), arXiv:2008.12780 [astro-ph.HE].
[5] P. Lu, V. Takhistov, G. B. Gelmini, K. Hayashi, Y. Inoue, and A. Kusenko, Astrophys. J. Lett. 908, L23 (2021), arXiv:2007.02213[astro-ph.CO].
[6] V. Takhistov, P. Lu, G. B. Gelmini, K. Hayashi, Y. Inoue, and A. Kusenko, (2021), arXiv:2105.06099 [astro-ph.GA].
[7] R. Laha, P. Lu, and V. Takhistov, Phys. Lett. B820, 136459 (2021), arXiv:2009.11837 [astro-ph.CO].

44

Kavli IPMU Annual Report 2020

Figure 1. The chemical abundance pattern of the supernova remnant Sagittarius A, EAST for the data points. Here [Z/Fe]=log10 (X(Z)/X(Fe)) – log10 (X(Z)/X(Fe)) with X(Z) is the mass fraction of the element Z and  indicates the solar
value. The abundance ratios of Cr, Mn, and Ni relative to Fe are well-reproduced by the pure deflagration (PTD)
9−3model that occurs in the Chandra mass white dwarf with the central density of ~5×10 g cm (PTD5: solid line).
9−3

Other lines PTD2-PTD5.5 show the abundance patterns for the WDs with central densities of 2-5.5×10 g cm .

Kavli IPMU Annual Report 202045

Research Highlights
The other supernova remnant is 3C397. We have collaborated with the X-ray astronomy group at ISAS/JAXA who observed
3C397. They obtained the abundance pattern and found that the Ti/Fe and Cr/Fe ratios are much higher than the solar
ratios. This implies that the supernova ejecta is highly-neutronized by electron capture at such a high central density as
5×109 g cm−3, which also implies that the progenitor WD is the Chandra-mass WD, not sub-Chandra WD. Other element
ratios indicate that the explosion is of ordinary Type Ia rather than Iax. These results imply that the X-ray observations ofsupernova remnants to determine the abundance pattern is a very efficient approach to identify the progenitor WDs.
2. Light Variations of Betelgeuse and Its Implications
Betelgeuse is a red-supergiant which is an evolved massive star. It is normally one of the brightest, most recognizable starsof the winter sky, marking the left shoulder of the constellation Orion. But lately, it has been behaving strangely: an unprecedentedly large drop in its brightness has been observed in early 2020 (Figure 2), which has prompted speculation that
Betelgeuse may be about to explode.
We analyzed the brightness variation of Betelgeuse with the international team by using evolutionary, hydrodynamic andseismic modelling. We obtained that its radius is ~750R8(solar radius), which is smaller than the expected radius of ~1000R8
at the pre-supernova stage. We then concluded that Betelgeuse is in the core helium-burning phase, which is more than
100,000 years before a supernova explosion happens. It has smaller mass (16.5–19M8) and radius and is 25 percent closer
to Earth (530 light years) than previously thought.
We showed that smaller brightness variations of Betelgeuse (Figure 2) have been driven by the so-called kappa-mechanismof stellar pulsations, and suggested that the large dip in brightness in early 2020 (Figure 2) is unprecedented, and is likely
due to a dust cloud in front of Betelgeuse.

4. Fast Blue Optical Transient (FBOT): COW and GEP
Compared with normal core-collapse SNe (Types II, IIb, Ib), appearing ten to a hundred times brighter at its peak, and witha much faster rise toward the peak (~1–3 days), optical transients AT 2018cow (nicknamed COW) and SN 2018gep (GEP)
represent a new type of supernova called Fast Blue Optical Transient (FBOT) (Figure 4).
We have succeeded to explain such an extreme property of COW and GEP as a collision between the supernova and circumstellar materials with no-hydrogen which were ejected before the explosion (Figure 4). In particular, we suggested thatsuch He and C-rich circumstellar materials were ejected from very massive stars which have the initial masses of 80–140M8
and undergo big pulsations caused by electron-positron pair production just before the core-collapse.
These circumstellar materials are dense and opaque, making the radius of the star effectively large. When the supernova
explosion occurred due to core-collapse, a strong shock wave propagated through the circumstellar materials. When it
reached the surface, its kinetic energy was converted into radiation energy, causing a sudden and a very bright event tooccur thanks to the large radius. This mechanism can explain the very fast rise of the observed brightness. For the smaller
mass of circumstellar materials, the decline of the light curve is also faster.
We are proposing that the variation of the circumstellar mass formed from the pulsational pair-instability of very massive
stars would cause variation among FBOTs. If the circumstellar mass is large enough, the resulting supernova would beobserved as a so-called Superluminous Supernova which is bright, but shows much slower rising. Such a massive star isrelated to the formation of massive Black Holes observed by the gravitational wave and also related to the First Stars in theuniverse.

Research Highlights

3. Electron Capture Supernovae of Super AGB Stars
Electron-capture supernovae have been predicted by K. Nomoto and collaborators in the early 1980s to arise from the
explosions of massive “super-asymptotic giant branch (SAGB)” stars whose main-sequence masses are ~8-10M8 (Figure 3).
However, there has been scant clear evidence.
The observational team led by the group of Las Cumbres Observatory in Santa Barbara found that the supernova SN
2018zd had many unusual characteristics, some of which were seen for the first time in a supernova. We have collaborated
with the observer group. We noticed that SN 2018zd had all six indicators predicted for electron capture supernovae,
namely, (1) an apparent SAGB progenitor, (2) strong pre-supernova mass loss, (3) an unusual stellar chemical composition,(4) a weak explosion, (5) little radioactivity, and (6) a neutron-rich core. This indicates that an electron capture supernova was
finally discovered after 40 years since its existence was predicted by K. Nomoto and collaborators.

Figure 4. The observed light curves of AT 2018cow (COW) and SN 2018gep (GEP) are shown by
the filled circles and squares, respectively. The solid lines show the light curve models for
COW (green) and GEP (red). For comparison, the dashed lines show the observed light
curves of Type Ia supernova SN 2011fe (green) and Type Ibc supernova SN 2006fo (red).
The COW and GEP are much brighter than Type Ia and Ibc supernova at early phase.

46

Figure 2. Recent brightness variations of Betelgeuse. A comparison of direct

Figure 3. An artist’s impression of the “electron capture” supernova. It shows

images of the surface of Betelgeuse between Jan 2019 and Dec

how an imaginary deep-sea fish “football-fish” (having Neon-Sign)

2019 show that large portions of the star faded in Dec 2019, whicheats away at the electrons, which induces the collapse of the elec-

could indicate a dust cloud appearing in front of it.

tron-degenerate O+Ne+Mg core of the 8–10 M super-AGB star.

Kavli IPMU Annual Report 2020

Kavli IPMU Annual Report 2020

47

6

AWARDS

AwardsKavli IPMU Senior Scientist Ken’ichi Nomoto awarded the Order of the Sacred
Treasure
Ken’ichi Nomoto, University of Tokyo Emeritus Professor and Kavli Institute for the Physics and Mathematics of the
Universe Senior Scientist, has been selected as one of the recipients of the Order of the Sacred Treasure, it wasannounced by the Japan government on April 29 as part of the 2020 Spring Conferment.
Nomoto has been a worldwide leader in astronomy, developing theoretical work that has helped researchers study
the last stages of stellar evolution, supernovae, nucleosynthesis, gamma ray bursts, neutron star evolution, and thechemical evolution of galaxies amongst many things. A keen educator, Nomoto has also spent a significant amountof time teaching young students and spreading interest in the subject.

Kavli IPMU Visiting Senior Scientist Alexander Kusenko and Visiting Scientist Christian Schnell
Selected as 2021 Simons Fellows
On February 4, 2021 (local time in the US), the Simons Foundation of the United States announced the 2021 Simons Fellows. The selected
researchers included Professor Alexander Kusenko of the University of California, Los Angeles, and Professor Christian Schnell of the State
University of New York at Stony Brook.
Established by James and Marilyn Simons in 1994, the Simons Foundation is an organization that supports science and science education,
including supporting researchers via the Simons Fellowship. The fellowship is awarded to tenured professors at a university in the United States
or Canada with outstanding achievements in mathematics or theoretical physics. Simons Fellows can extend their sabbatical period from asemester to a year, allowing them time to focus solely on long-term research. Professor Kusenko and Professor Schnell were awarded Simons
Fellowships for theoretical physics and mathematics, respectively.

Kavli IPMU’s Tsutomu Yanagida Awarded 20th Particle Physics Medal of Japan

Principal Investigator David Spergel Elected President of Simons Foundation(Credit: Chiaki Hikage)An international research team led by the Kavli Institute for the Physics and Mathematics of the Universe (Kavli
IPMU) Project Associate Professor Chiaki Hikage has received the 2020 PASJ Excellent Paper Award, an honour givenby the Astronomical Society of Japan (ASJ).
The PASJ Excellent Paper Award recognizes particularly outstanding papers published within the previous five years
in ASJ’s journal, the Publications of the Astronomical Society of Japan (PASJ). The award-winning papers not only
have to be original; they must also have made significant contributions to astronomy.
The award honors all the authors and their institutions, including the University of Tokyo; Nagoya University; Princeton University; Carnegie Mellon University; and the Academia Sinica Institute of Astronomy and Astrophysics(ASIAA), Taiwan. The award-wining paper, “Cosmology from cosmic shear power spectra with Subaru Hyper
Suprime-Cam first-year data,” was published in 2019.

On December 17, 2020 (local time in the US), the Simons Foundation in the United States announced that Kavli
Institute for the Physics and Mathematics of the Universe (Kavli IPMU) Principal Investigator (PI) David Spergel will
become the next president of the foundation from July 1, 2021. The Simons Foundation was established in 1994 by
James Simons and Marilyn Simons to support science and science education.
PI Spergel’s research interests range from exoplanet exploration to mapping the early Universe and the formationof galaxies, including as a leading research member of the Wilkinson Microwave Anisotropy Probe (WMAP), a pioneering satellite initiative that has made precise observations of the cosmic microwave background. The WMAP has
had a significant impact on science, such as greatly improving our knowledge about the density fluctuations that
seeded the formation of galaxies. In recognition of his research, PI Spergel has received numerous awards, including
the 2018 Breakthrough Prize in Fundamental Physics.

Other prestigious awards
Recipient's nameShunsaku Nagasawa

48

Kavli IPMU Annual Report 2020

AwardsChiaki Hikage and Others Win the 2020 PASJ Excellent Paper Award

In September 2020, Kavli IPMU Visiting Senior Scientist Tsutomu Yanagida was awarded the 20th Particle Physics Medal of Japan. The award isconferred by the Particle and Nuclear Theory Forum of the Physical Society of Japan to persons who have given long-term and important
contributions to the development of particle physics theory.
Yanagida’s award-winning achievement was in recognition of his work in a paper titled “Formulation of a Hidden Local Symmetry and its
Application to Hadron Physics.” In a prior publication—titled “Is the ρ Meson a Dynamical Gauge Boson of Hidden Local Symmetry?”—Yanagida and his collaborators succeeded in formulating a hidden local symmetry in QCD (quantum chromodynamics), and proposed the ρ meson
as a composite gauge field.

Name of Award
School of Science Encouragement Award (Master program)

Kavli IPMU Annual Report 2020

49

Invited talks given by the Kavli IPMU researchers (Selected 10 of 132)

Conference title
Date, PlaceHyper-K Technical Coordination Meeting
18-21 May 2020, [Online]

73
(32)
54
(40)

19th International Conference on B-Physics at Frontier Machines (Beauty 2020)

346
(332)

The World of Mathematical Physics

223
(2)

6 July - 14 August 2020, [Online]
21-24 September 2020, [Online]
6-7 November 2020, [Online]

CMB Systematics and Calibration Focus Workshop

228
(190)

Time-domain Cosmology with Strong Gravitational Lensing

114
(95)

What is Dark Matter? - Comprehensive Study of the Huge Discovery Space in Dark Matter

293
(14)

12th PFS Collaboration Meeting

134
(72)

30 November-3 December 2020, [Online]

25 January - 2 February 2021, [Online]

9-11 March 2021, [Online]

50

Attendees(from abroad)

McKay Correspondence, Mutation and Related Topics

6 February 2021, [Online]

Kavli IPMU Annual Report 2020

8

CONFERENCE PRESENTATIONSAND SEMINAR TALKS
Date

Presenter

Presentation title

Conference name

Leicester Algebra and Geometry
Open Online Seminar (LAGOON)

Jul. 2, 2020

Hiraku Nakajima

Euler numbers of Hilbert schemes ofpoints on simple surface singularities
and quantum dimensions of standard
modules of quantum affine algebrasAug. 14, 2020

Yukinobu Toda

On d-critical birational geometry andcategorical DT theories

AGEA seminar

Aug. 31, 2020

Yevgeny Stadnik

Search for very low mass feeblyinteracting particles (atomic physics,
quantum technology)

CERN online workshop on "FeeblyInteracting Particles"

Oct. 23, 2020

Yukari Ito

The McKay correspondence

Kinosaki Algebraic Geometry
Symposium 2020

Oct. 26, 2020

Hitoshi Murayama

The Higgs boson and theunderstanding of the Universe

Higgs 2020

Nov. 19, 2020

Hsueh-Yung Lin

Algebraic approximations of compact
Kähler threefolds

Workshop on birational geometry

Dec. 9, 2020

Tom Melia

New analytic probes of effective field
theoryNCTS Annual Theory Meeting 2020

Dec. 14, 2020

Mark Vagins

DSNB Detection with a Gadoliniumloaded Super-Kamiokande

SNEUNW20 - Supernova and Early
Universe Neutrinos Workshop(SNOWMASS NF04)

Jan. 15, 2021

Naoyuki Tamura

Subaru Prime Focus Spectrograph: A
next generation facility instrument of
the Subaru telescope is coming to FirstLight

237th American Astronomical
Society meeting

Feb. 24, 2021

A New Window into Neutrino
Astronomy with Dark Matter
XIX International Workshop on
Volodymyr Takhistov
Experiments: Supernova Forecast and Neutrino Telescopes
the Origin of Supermassive Black Holes

Kavli IPMU Annual Report 2020

Conference Presentations and Seminar Talks

7

CONFERENCES

51

9

OUTREACH AND
PUBLIC RELATIONS
DATE

VENUE

number ofparticipants

May 30, 2020

Online643"A Prism to Unveil the Universe"

May 30, 2020

Online423"A Way to Look at the Universe"

May 31, 2020

Online414"In Search of the Theory of Everything"May 31, 2020

Online415

Fundamental Talks (online), Vol. 01: Mathematics—how to interact with
objects in a non-everyday mannerAug. 2, 2020

Online93

Kavli IPMU x ICRR Joint General Lecture: “Explorations of the unknown andouter-most limits of the Universe and a New Physics”

Aug. 8, 2020

Online700Aug. 4,6,8-9, 2020

Online108

Sep. 22, 2020

Online20

Oct. 18 & 25, 2020

Online1,302

5th “Actually I Really Love Physics!”–Career Paths of Female Physics Graduates

Nov. 7, 2020

Online18

SECRETS OF THE SURFACE online film screening + panel

Nov. 8, 2020

Online204

Kavli IPMU x ICRR Joint Public Lecture: “New era of Space telescopes”

Nov. 22, 2020

Online563

Science Cafe "Universe"

Dec. 5, 2020

Online51

World-class Researchers are Coming from WPI!

Dec. 26, 2020

Online70

WPI Science Symposium 2021 "Life" in the 21st Century

Feb. 7, 2021

Online686

The 6th Kavli IPMU, ELSI, and IRCN Joint Public Lecture: “A Question of Origins”

Feb. 28, 2021

Online586

EVENT TITLE

Kavli IPMU Monoshiri Newspaper Online Talk Series"Seeing the World with Mathematics"

Collaborative Knowledge Creation
Practical Learning Course with the University of Tokyo CoREF "Learning andCreating Physics - From High School to the Forefront Research of the Universe"
Science Cafe "Universe"
Kashiwa Campus Open Day, 2020

52

Kavli IPMU Annual Report 2020

April 2020–March 2021

5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8583, Japan

TEL: +81-4-7136-4940

FAX: +81-4-7136-4941 http://www.ipmu.jp/

ISSN 2187-7386

Printed in Japan

Kavli IPMU

Annual Report 2020

Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU)
The University of Tokyo Institutes for Advanced Study
The University of Tokyo