LETTERI NST I T U TE FOR A DVA NCED R ESE A RCHMarch 2019 Vol. 17

Special Interview

Exploring the Frontiers of Research to Pursue the Mystery of
How Living Organisms Measure Time of a Day
Takao Kondo
Research Highlights

INSTITUTE FOR ADVANCED RESEARCH, NAGOYA UNIVERSITY
Telephone. +81-52-788-6051

Facsimile. +81-52-788-6151

E-mail. iar@adm.nagoya-u.ac.jp

http://www.iar.nagoya-u.ac.jp/

The Origin of European Formal Gardens / Yukiko Kawamoto
A Delicate Molecular Orchestration to Create Functional Stomata / Soon-Ki Han
Exploring Quantum Spacetime / Yuki Sato
Trilateral Relationships among Japan, Korea and China in 17th-19th Centuries / Yongchao Cheng
SRPP, a Cell Wall Protein is Involved in Development and Protection of Seeds and Root Hairs. / Natsuki Tanaka
Degenerations in Infinite Dimensional Teichmüller Spaces / Hiroki Fujino
Direct Dark Matter Search With XENON / Shingo Kazama
Searching for New Physics through Precision Flavor Physics / Teppei Kitahara

Yuki SATO

Research Highlights _ 03

Exploring Quantum Spacetime

Trilateral Relationships among Japan,
Korea and China in 17th-19th Centuries

Yuki SATO

Yongchao CHENG

Designated Assistant Professor of Young Leaders Cultivation Program
Graduate School of Science / Institute for Advanced Research, Nagoya University
E-mail: ysato@th.phys.nagoya-u.ac.jp

Designated Assistant Professor of Young Leaders Cultivation Program
Graduate School of Humanities / Institute for Advanced Research, Nagoya University
E-mail: yongchao@nagoya-u.jp

INTRODUCTIONINTRODUCTION
Elementary physics mostly incorporates Einstein’s theory of generalrelativity and quantum mechanics. The former associates gravity with thebending of space and time, collectively called spacetime, and the latter explains thecharacteristic properties of matter at short distances. According to generalrelativity, spacetime curves due to the existence of matter, and matter exhibits
quantum characteristics at short distances. Therefore, spacetime and gravity aresupposed to exhibit quantum mechanical effects and those effects become
important around the Planck scale, which is a length of about 10–35 meters. My
field of research is the search for a theory that describes the quantum effects ofgravity, dubbed quantum gravity. The study of quantum gravity is importantbecause it would allow us to understand how the Universe began: spacetime withall kinds of matter may be viewed as a “flip book” made out of the Universe ateach instant of time, and the Universe is known to be expanding faster and faster.
Going back in time, the size of the Universe at its “beginning” was about the
Planck scale, and therefore the physical laws in this epoch can be explained byquantum gravity.

DIFFICULTIES
Combining general relativity and quantum mechanics based on“conventional” methods encounters notorious inconsistencies. According to thelaws of quantum mechanics, investigating short scales requires large amounts ofenergy, and up to the present we are unable to create enough energy to investigate
the Planck scale. The theoretical and experimental difficulties of doing this makethe construction of quantum gravity complex.

STRATEGY
There exist various candidates for quantum gravity, but I am most interested
in the approach based on statistical mechanics known as Causal Dynamical
Triangulation, abbreviated to CDT [1]. In the CDT approach, spacetime isdiscretized by special simplices (see Fig. 1). Quantum mechanical effects ofspacetime or gravity can be taken in by the statistical sum over “all possible
shapes” of spacetime. Compared to the other candidates, the gee-whiz advantagesof the CDT approach are that they allow us to explore the qualitative features ofspacetime at the Planck scale and to reproduce the current expanding Universe bycomputer simulation. However, there are real limitations to machine power. To
understand the laws that govern physics at the Planck scale, we need to do
analytic computations, but we do not know how to do them at the moment.
Constructing a method to deal with CDT analytically is of great significance as it
will allow us to study the laws of Planck-scale physics quantitatively. When facing
an abstruse problem, it is often helpful to simplify the problem to gain an insight
into its true nature. I use Dynamical Triangulation, abbreviated to DT, in two
spatial dimensions as a simplified model, although the dimensions of real
obser ved spacetime are four—three spatial and one temporal. Since
two-dimensional DT can be studied analytically, my strategy is to closely examine
this two-dimensional model to find a technique for dealing with a realistic CDT
approach in four dimensions.

09 | IAR LETTER | March 2019

Yongchao CHENG

Research Highlights _ 04

F i g u re : F ro m t h e l e f t , t h e f i g u re d e p i c t s t w o - , t h re e - a n d ( o n e o f )four-dimensional simplices. The red and blue lines indicate the temporal andspatial edges.

ZERO-TEMPERATURE CRITICALITY
We couple Ising spins as matter with two-dimensional DT and call thismodel the Kazakov model [2]. Since the Ising spin that mimics, for instance, themagnetic moment of an atom is a simple but non-trivial matter, we use theKazakov model for this purpose. In the Kazakov model, reducing the criticaltemperature at which the Ising spin interaction becomes long range down toabsolute zero temperature, we have tried to single out quantum effects, because atabsolute zero only quantum fluctuations survive. Amazingly, the temporal
direction “emerges” by cooling down the temperature and spacetime at the criticaltemperature of absolute zero “resembles” that obtained in the CDT approach [3].
A similar procedure was first discussed in [4, 5].

FUTURE DIRECTION
Dealing with DT in four spatial dimensions analytically seems far more
tractable than the analytic study of CDT in four spacetime dimensions. In
addition, according to our observations in the Kazakov model, the cool-down
process may induce the temporal direction. Thus, once we construct a way to
study four-dimensional DT analytically, we may have a chance to understand theproperties of Planck-scale physics quantitatively by cooling the criticaltemperature down to absolute zero. Needless to say, this possibility is quite
fascinating.

Joseon Korea, a kingdom caught between Tokugawa Japan and twoconsecutive dynasties of China, the Ming and the Qing, played a very importantrole in building diplomatic relations between the two in the first half of theseventeenth century. It contributed almost as much as it sabotaged. Throughout
the early modern period, Tokugawa Japan and Ming-Qing China were connectedby Joseon Korea, but the same country constantly tried to hamper progress.

RESEARCH BACKGROUND

Succeeding to country unified by his father, the second emperor Hong Taiji
consolidated power within and declared a new dynasty—the Qing. The emperor
ruled that establishing official diplomatic relations with Japan would be
beneficial, but the consequences of the dynastic changes from Ming to Qing
meant that efforts to that end yielded nothing concrete. The state of bilateralrelations at that time has been called “silent diplomacy” (by Iwai Shigeki) or“non-diplomatic relations” (by Sugeyama Kiyohiko).
When we turn our sights on Japan, in the 1630s the bakufu imposed aprohibition on overseas voyages and limited foreign contact to the four ports ofNagasaki, Tsushima, Satsuma, and Matsumae. However, when we examine thissituation from the perspective of the continent, we find that China wasconnected to Japan through the mediation of Joseon Korea and the Ryukyu
Kingdom in the early-modern period. Research on the diplomatic situation in the
Ryukyu Kingdom and cultural exchanges occurring via the Ryukyu Kingdom has
been plentiful. However, the Sino-Japanese connection through Joseon, the mostloyal vassal state of Ming China and later Qing China, has received far lessattention.
Why were diplomatic relations between Japan and China not restored andbecame dependent on the mediation of secondary countries? The primary cause
was the Japanese invasion of Korea (1592–98), which disturbed the oldinternational order in East Asia. Japan’s restoration of diplomatic relations with
Ming China, which formed part of post-war normalization, contributed to theestablishment of diplomatic channels between Japan, China and Korea.

RESTORATION PROCESS

References（1）J. Ambjorn, A. Goerlich, et al., “Nonperturbative Quantum Gravity,” Phys. Rept.
519,（2012）127.
（2）V. A. Kazakov, “Ising model on a dynamical planar lattice: Exact solution,” Phys.
Lett. A 119,（1986）140.
（3）Y. Sato and T. Tanaka, “Criticality at absolute zero from Ising model on
two-dimensional dynamical triangulations,” Phys. Rev. D 98,（2018）No. 2, 026026.
（4）J. Ambjorn, R. Loll, et al., “A New continuum limit of matrix models,” Phys. Lett. B
670,（2018）224.
(5) J. Ambjorn, Y. Sato, et al., “New multicritical matrix models and multicritical 2d
CDT,” Phys. Lett. B 712 (2012) 109.

coexistence of multiple intermediaries mentioned above (before 1615), and theperiod when Korea was the sole mediator (after 1615).

At the dawn of the Tokugawa bakufu, Tokugawa Ieyasu attempted toreconstruct diplomatic relations with Ming China through three channels: (1)Ming merchants visiting Nagasaki, (2) Joseon Korea, and (3) the Ryukyu
Kingdom. However, (1) and (3) did not bring good results, with only attempt (2)bringing results. However, scholars have not investigated (2) to the same extent as
the other two.
In this project, I have investigated the diplomatic process and real situation
surrounding how Tokugawa Japan attempted to restore diplomatic relations with
Ming and Qing China via Joseon Korea in the seventeenth century.
Since the Tokugawa bakufu had already given the Tsushima domain theright to manage Joseon affairs, in examining Japan’s attempt to restore relations
with China, the activities of the Tokugawa bakufu and Tsushima domain should
be discussed separately. This process is divided into two periods: the period of

Figure: Relationships between Japan, Korean and China in the early modern
periodJOSEON KOREA: THE SOLE MEDIATOR

After Jurchen Manchu’s invasion of Korea in 1627, the only
bakufu-sanctioned envoy sent to Seoul in the early-modern period was Kihaku
Genpo, a diplomat-monk from the Tsushima domain, in 1629. Deciphering his
manuscripts, including letters written by Genpo recorded in “Zenrin Tsusho,”
Genpo’s diary “Hochoro Jokyo nisshi,” and the reception record “Eumbing haenggi”
which have been largely ignored by researchers up to the present, we havediscovered that restoration of diplomatic relations was not ordered by the bakufu
in the 1629 mission, but was used by Tsushima as an excuse to visit the capital of
the Joseon Dynasty. Also, since Qing China was suspicious of Joseon’s relationshipwith Japan, Joseon did not report to Qing China on Tsushima’s expectations forthe restoration of diplomatic relations.

OVERVIEW

From my empirical analysis, I demonstrate that placing Joseon Korea as amediator between Tokugawa Japan and Ming-Qing China, who had notestablished formal diplomatic relation in the 17th–19th centuries, allowed China
and Japan to have mediated political connections. To truly understand thetrilateral relationship is not to build up bilateral relations between any of the two,even in a detail-oriented way. By sleight of hand, Joseon Korea benefited frombeing the mediating state, manipulating diplomatic relations between Japan andQing China to its own ends.

References（1）Ura Renichi, “Meimatsushinshyo no senman kankei jyo ni okeru nihon no chii,” 2 明末清初の鮮満関係上における日本の地位 (二), Shirin 史林 19(3), 1934, pp. 122-146

March 2019 | IAR LETTER | 10

Yukiko KAWAMOTO

Research Highlights _ 01

The Origin of European Formal Gardens

A Delicate Molecular Orchestration
to Create Functional Stomata

Yukiko KAWAMOTO

Soon-Ki HAN

Designated Assistant Professor of Young Leaders Cultivation Program
Graduate School of Humanities / Institute for Advanced Research, Nagoya University
E-mail: kawamoto.yukiko@c.mbox.nagoya-u.ac.jp

Designated Assistant Professor of Young Leaders Cultivation Program
Institute of Transformative Bio-Molecules, Nagoya University
E-mail: soonhan@itbm.nagoya-u.ac.jp

INTRODUCTIONINTRODUCTION

Stomata are tiny pores on the leaf surface in almost all land plants, which enablea plant to take in carbon dioxide to make food through photosynthesis and releaseoxygen that we breathe. Stomata also function as a water passage; open to evaporate
water and close under the dry condition to prevent water loss. In order for stomata toopen and close in response to the environment, an intact structure in which a pair ofguard cells surrounding the pore is essential. Proper gas and water exchange throughstomata greatly impacts the crop yield and water cycle in the atmosphere, which
eventually influence the sustainability of humanity. The functional stomata are
generated by a single symmetric division of a stomatal precursor known as guard
mother cells or (GMCs), however, it was not known how this event is coordinated.
Our research published in the American scientific journal Developmental Cell in
May 20181 elucidated the mechanism by which only one symmetric cell divisionoccurs for functional stomata through the genetics, molecular biology, bioinformatics
and mathematical modelling.

It is believed that European formal gardens, especially those adorned withclipped trees (topiary) and plants arranged in geometrical patterns, have their
origins in Roman gardens. This understanding is based on the evidence of ‘opus
topiarium’ and trimmed plants in Latin texts, although it is known that the‘topiarius’ is not what ‘topiary’ means in a modern sense. Wall paintings, textual
evidence, and excavated Pompeian gardens suggest that the Romans had densely
planted gardens resembling natural groves, challenging our previous conceptionof Roman gardens. My research explores how the Romans perceived anddescribed their gardens, and whether Roman gardens can be the origin ofEuropean formal gardens.

GARDENS IN POMPEIIWhen Wilhelmina F. Jashemski, an American classicist who had green
fingers, decided to study Roman gardens in the early-1950s, it was not a topic
which received scholarly attention. Pierre Grimal, a French classicist who
wrote a book on Roman gardens in 1943, is an exception but he did notfeature examples of uncovered gardens in Pompeii, which had already beenreported by Italian and German excavators since the end of the nineteenth
century. Jashemski first envisaged writing a monograph covering all the
known textual and archaeological examples of Roman gardens, but she soon
realised the scale of this challenge. Instead, she started excavating gardens in
Pompeii and neighbouring sites, and collaborated with archaeologists,archaeobotanists, ornithologists, natural scientists, and others. Based on theoutcomes of her excavations, she edited volumes on Pompeian gardens whichbecame sources of information for later scholars.
The excavations in Pompeii made Jashemski realise that many Roman
gardens were not formal gardens, because plant root cavities discovered ingardens suggest that the plants did not form geometric patterns. (cf. organic
substance such as roots decayed gradually following the eruption of Mt.
Vesuvius in 79 CE and made cavities inside volcanic deposits. It is well known
that a famous Pompeianist Giuseppe Fiorelli poured plaster into cavities andmade plaster casts of victims.) Her observation was followed by Annamaria
Ciarallo, a Pompeianist, whose analyses suggested that Pompeian gardens
were often reconstructed in the styles popular at the time of excavation. In thecase of Casa degli Amorini Dorati (Figure), archaeologists referred tosculptural finds but there is no mention of the garden patterns in the
excavation reports Notizie degli Scavi (cf. the wreaths and oscillae hanging in
the colonnade are based on depictions on wall paintings). Nevertheless, thegarden was reconstructed as if it had been a formal garden.

TEXTS, WALL PAINTINGS, AND EXCAVATION

Following in Jashemski and Ciarallo’s footsteps, excavators in the 21st
century recognised that the appearance of Roman gardens envisaged by scholars
in previous centuries should be revised. Kathryn Gleason, for example, hasaffirmed this view in her excavation at the Villa Arianna in Stabiae. I also analysed
garden wall paintings and classical literary sources and argued that Roman
gardens had a more naturalistic appearance.
07 | IAR LETTER | March 2019

Soon-Ki HAN

Research Highlights _ 02

MASTER REGULATORS OF STOMATAL DEVELOPMENT

Figure: Casa degli Amorini Dorati, Pompeii. After the reconstruction. (Credit:
P.Grunwald, Neg. D-DAI-Z-83.2037. Deutsches Archäologisches Institut Rom)

However, the question remains: ‘Why did we start thinking that Roman
gardens are the origin of European formal gardens?’ By using archaeological andtextual evidence, I am trying to answer this question during my fellowship at theInstitute for Advanced Research, Nagoya University.

TAKING A STEP FURTHER

Stomata emerge from uniformed cells on the leaf surface. The subset of cells
is committed to the stomatal lineages and undergoes a series of controlled cell
division and differentiation to form mature guard cells. In Arabidopsis plants, eachstep of the stomatal lineages is mediated by the sequential action of transcription
factors; SPCH, MUTE and FAMA, and SCREAMS2 . Transcription factors
behave like a switch that can control the “on” or “off ” state of other plant genes inorder to make sure gene expression happens in the right place, time and amountfor the accurate developmental decision upon signal sensing. Among these threetranscription factors, when MUTE is forcibly expressed, the plant surface is sorely
composed of stomata (Fig. 1B), while no stomata are formed when plants lose
MUTE gene activity (Fig. 1C). Therefore, we hypothesized that MUTE instruct
the gene expression program to create stomata and wanted to comprehensively
identify the genes controlled by MUTE.

My project ‘European Gardens: Origins, Reception, and Reconstruction’is generously supported by the Program for Fostering Researchers for the Next
Generation ( Japan Science and Technology Agency). In this project, I shallcollaborate with historians and natural scientists based at Hokkaido, Tohoku,
and Nagoya Universities. Through this project, I aim to study how scientificanalyses of archaeological finds are conducted and how one should interpretthe results provided by natural scientists.
Figure 1: Close-up images of the leaf surface of Arabidopsis plants, taken using
a microscope.（A）A typical arrangement of stomata across the surface.（B）Arabidopsis strain that artificially produces a lot of the MUTE protein, and has
many abnormal stomata as a result.（C）Arabidopsis strain that lacks MUTE
gene activity. Scale bars are 50 micrometers.

MUTE INDUCES BOTH CELL CYCLE GENES
AND THEIR REPRESSORS
References（1）Grimal, P.（1943）Les jardins romains a la fin de la republique et aux deux premiers
siecles de l'empire. Essai sur le naturalisme romain.
（Paris）（2）Jashemski, W. F.（1979, 1993）The Gardens of Pompeii: Herculaneum and the Villas
Destroyed by Vesuvius, 2 vols.
.
（New Rochelle）（3）Jashemski, W. F. and Meyer, F.（eds.）（ 2002）The Natural History of Pompeii.
（Cambridge）（4）Jashemski, W. F., Gleason, K., Hartswick, K. J., and Malek, A.-A.（eds.）（ 2017）
Gardens of the Roman Empire.
（Cambridge）

Thanks to the Next Generation Sequencing technology and bioinformatics,
we could easily identify which genes the MUTE protein turned on or off by
employing a strain of Arabidopsis (Fig. 1B) in which we can manipulate toproduce a lot of MUTE protein. It turned out that MUTE is the potent inducerof the cell cycle factor necessary for the symmetrical division of GMCs. Amongthem, Cyclin D5 (CYCD5) was identified as a direct target of MUTE.
Unexpectedly, we found that MUTE directly induces expression of sistertranscription factor FAMA and another type of transcription factor FOUR LIPS
(FLP). Both FAMA and FLP are known to have an inhibitory action on
symmetric cell division. These findings show that MUTE induces both activatorsand repressor of GMC division. Why would MUTE do this?

Figure 2:（A, B）Regulatory network orchestrated by MUTE drives the single
symmetric cell division to create functional stomata and（C）Typical stomata:paired guard cell（D, E）abnormal stomata produced by genetic perturbation of
the network.

MODE OF CONTROL BY MUTE

Through precise experiments, we obtained data on the timing MUTE
activation of these activators and repressors of cell division; premature expressionof the repressor (FAMA or FLP) produces a single guard cell (Fig. 2D) andprolonged or precautious expression of the activator (CYCD5) yields extra cell
division (Fig. 2E). We also incorporated this information into a mathematicalmodel and simulated how MUTE acts to both activate and repress cell division in
the GMC. MUTE first turns on the cell cycle activator including CYCD5, which
triggers one round of cell division. Then,
FAMA and FOUR LIPS induced by MUTE
act to prevent further cell division, yielding one
functional stomata consisting of two guard
cells (Fig. 2A). The result shows that MUTE
drives a tightly orchestrated sequences ofactivation and repression (Fig. 2B) that ensures
one and only one single cell division to createfunctional stomata. This mode of control by
MUTE is known as a feedforward circuit,which is widely seen in rapid gene expression
control of animals, yeast and bacteria togenerate sharp output in developmental
processes3. Therefore, this research is close to
the fundamental principle of making shapes Figure 3: MUTE is a conductor
f the delicate molecularregardless of organisms, and it is expected to osymphonyof stomatal developcontribute to crop improvement through the ment in Arabidopsis. Keiko Torii
and her daughter Erika.
control of stomata development.
References（1）Han, S.K., Qi, X., Sugihara, K., Dang, J.H., Endo, T.A., Miller, K.L., Kim, E.D.,
Miura, T., Torii, K.U. MUTE Directly Orchestrates Cell-State Switch and the Single
Symmetric Division to Create Stomata. Dev Cell. 45, 303-315（2018）（2）Han, S.K., and Torii, K.U. Lineage-specific stem cells, signals and asymmetries
during stomatal development. Development 143, 1259–1270,（2016）（3）Basu, S., Mehreja, R ., Thiberge, S., Chen, M.T., and Weiss, R .（2004）.
Spatiotemporal control of gene expression with pulse-generating networks. Proc. Natl.
Acad. Sci. USA 101, 6355–6360,（2004）

March 2019 | IAR LETTER | 08

Natsuki TANAKA

Research Highlights _ 05

SRPP, a Cell Wall Protein is Involved in Development and Protection of Seeds and Root Hairs.

Hiroki FUJINO

Research Highlights _ 06

Degenerations in Infinite Dimensional
Teichmüller Spaces

Natsuki TANAKA

Hiroki FUJINO

Designated Assistant Professor of Young Leaders Cultivation Program
Graduate School of Bioagricultural Science / Institute for Advanced Research, Nagoya University
E-mail: tanaka.natsuki@h.mbox.nagoya-u.ac.jp

Designated Assistant Professor of Young Leaders Cultivation Program
Graduate School of Mathematics / Institute for Advanced Research, Nagoya University
E-mail: m12040w@math.nagoya-u.ac.jp

IDENTIFICATION OF SRPP

Root hairs are involved in major root functions such as the absorption ofwater, acquisition of nutrients, and secretion of organic acids and enzymes (Ref.
[1]). Enhancement of root hair development in response to a phosphate (Pi)
deficit has been reported extensively. Our studies revealed that the expression ofplasma membrane phosphate transporters and the secretion amounts of acidphosphatase and organic acids markedly increased in long root hairs under
Pi-deficient conditions. These emergently elongating root hairs may provide
good material for understanding the maintenance mechanism of the structureand function of root hairs. We performed a proteomic analysis using a root
hair-less line to identify new types of proteins that keep the structure andfunction of root hairs, and identified a protein (Seed and Root Hair Protective
Protein, SRPP) that was induced in root hairs under Pi-deficient conditions.

PHYSIOLOGICAL FUNCTION OF SRPP

Promoter assay and mRNA quantification revealed that SRPP wasexpressed not only in root hairs but also in seeds. Considering thetissue-specific expression, we focused our attention on the physiological roleof SRPP and investigated the phenotypic properties of root hairs and seeds ofa transposon-tagged knockout mutant, srpp-1, which consistently displayed
defects in root hairs and seeds. Root hairs in srpp-1 were short and most ofthem were dead under Pi-deficient conditions. In addition to root hairs, mostsrpp-1 seeds were withered and their embryos were dead (right side of figure).
SRPP tagged with green fluorescent protein was detected in the cell wall.
Electron microscopy showed abnormal morphology of the cell wall of srpp-1(left side of figure). Wild-type phenotypes were restored when the SRPP gene
was expressed in srpp-1. These results strongly suggest that SRPP contributes
to the construction of robust cell walls, whereby it plays a key role in thedevelopment of root hairs and seeds (Ref. [2]).

ENH A N CE M EN T OF SR PP E XPR E SSI ON DUR IN G
EMERGENT ROOT HAIR DEVELOPMENT

We analyzed the expression profile of SRPP during cell elongation ofroot hairs under Pi-deficient conditions and compared the transcript levels inseveral mutants with short root hairs. The mRNA level decreased in mutants
with short root hairs. Induction of SRPP expression by Pi starvation occurred
one or two days later than the induction of Pi-deficient sensitive genes such as
PHT1 and PHF1 (Ref. [3]). These results indicate that the expression of
SRPP is coordinated with root hair elongation. We concluded that SRPP isessential for the structural robustness of the cell walls of root hairs.

INTRODUCTION

I am Hiroki FUJINO, YLC
designated assistant professor for thisacademic year. My research is in thefield of mathematics, including
function theory, complex analysis,
metric geometry and similar fields. I
am currently particularly interested
in the degeneration of surfaces (more precisely, Riemann surfaces) in so-called
Teichmüller spaces. Inside Teichmüller spaces, surfaces can be stretched and bent.
Thus, surfaces generally degenerate into ‘‘surface-like objects’’ near the boundariesof the Teichmüller spaces, as shown in the following diagram. When we consider
infinite dimensional Teichmüller spaces, we can easily find many kinds of(strange) degenerations besides the above. I am studying these kinds ofdegeneration so that we will be able to deal with them logically and quantitatively.

OVEREXPRESSION OF SRPP IN SEED MATURATIONThe ratio of severe phenotypic srpp-1 seeds was dependent on thegrowth conditions. When the srpp-1 plants were cultivated at low humidity,
the defect ratio was 73%, which was higher than the 60% at normal humidity.
Therefore, we estimated that SRPP enhances the stress tolerance of seeds andtries to make overexpressors of SRPP using the 35S promoter. Overexpressionof SRPP enhanced the thermotolerance. In the heat treatment of seeds at 50°
C for 2 h, the germination rate of the seeds from the overexpressor wasincreased to twice that of the wild-type seeds (Ref. [4]). Under the same
conditions, no srpp-1 seed was germinated. The results indicate that SRPP isessential in siliques for producing normal viable seeds under stress conditions.
SRPP, a basic protein, may interact with acidic components such as pectinand be involved in construction of a robust cell wall. Seed integrity canpotentially be improved through modification of the SRPP gene.

RIEMANN SURFACES

A Riemann surface can roughly be described as a two-dimensional space
where the concept of an “angle” exists. For example, a sphere (like the surface ofthe earth) is a Riemann surface. In mathematics, Riemann surfaces are defined asconnected one-dimensional complex manifolds. This definition first appeared in
H. Weyl’s textbook in 1913. Since then (or from earlier, according to anotherdefinition), Riemann surfaces have been studied as an important concept inseveral fields of mathematics. Riemann surfaces are divided into two classes:
finite-type and infinite-type. Although I will not explain how to classify Riemannsurfaces here, as an example, a sphere is classified as a finite-type (see the figure
below for further examples).

TEICHMÜLLER SPACES

In the theory of Riemann surfaces, one of the most significant problems is
the Riemann moduli problem. This problem asks us, “How many Riemannsurfaces can be obtained by deforming a given Riemann surface?” This problem
has already been solved in several ways, but it was the Teichmüller theory thatanswered the problem rigorously and brilliantly. For a given Riemann surface, its
Teichmüller space is defined as the space containing all quasiconformal
deformations. For a swim ring in which g people can fit, the (complex) dimensionof its Teichmüller space is 3g-3.

DEGENERATIONSWhen quasiconformal
deformations come closer to theboundary of the Teichmüller space, theRiemann surface gradually degenerates.
C. McMullen proved that, for a
finite-type Riemann surface, almost alldegenerations are nodal surfaces. (Here,“a l m o s t a l l ” i s N O T i n t h emathematical sense. Mathematically, it
is correct to say that nodal surfaces are“dense” at the boundary.) A nodal surface is a kind of surface-like object, and iscertainly not a Riemann surface by definition (see the figure on the right).
Conversely, for some infinite-type Riemann surfaces, we can observe strange
degenerations. For example, the following figure shows a degeneration thatcannot occur in the case of a finite-type surface. The feature of this degenerationis that the degeneration surface is exactly a Riemann surface! You might think,“Should we call this a degeneration?” However, we can certainly prove that there
is no quasiconformal deformation from the initial surface to the degeneration
surface (Ref. [1]). Of course, many strange degeneration phenomena can befound besides this if we look at other infinite-type Riemann surfaces (Ref. [2]).
Understanding degeneration phenomena is one of the most important
problems in the deformation theory of Riemann surfaces. From the above
observations, the problem appears to be very complicated, but also interesting.

References

Figure legend. The cell wall protein SRPP is essential for the construction ofrobust cell walls. The knockout mutant srpp-1 shows defects in root hairs andseeds.

11 | IAR LETTER | March 2019

（1）Tanaka N., Kato M., Tomioka R. et al., Characteristics of root-hair less line of
Arabidopsis thaliana under physiological stresses. J. Exp. Bot. 65, 1497-1512（2014）.
（2）Tanaka N., Uno H., Okuda S. et al., SRPP, a cell wall protein is involved indevelopment and protection of seeds and root hairs in Arabidopsis thaliana. Plant Cell
Physiol. 58, 760-769（2017）.
（3）Uno H.,* Tanaka-Takada N.*（*co-first authorship）, Sato R. et al., Enhancement ofcell wall protein SRPP expression during emergent root hair development in Arabidopsis.
Plant Signaling & Behavior. 12, 10, e1368940（2017）.
（4）Uno H.,* Tanaka-Takada N.*（*co-first authorship）, Hattori M. et al., Physiologicalrole of a cell-wall protein SRPP in Arabidopsis seed maturation. J. Plant Research , 132:
145-154.（2019）.

QUASICONFORMAL DEFORMATIONS

Next, let us consider deformations of Riemann surfaces. Easy ways todeform a Riemann surface are by stretching and bending. Among suchdeformations, quasiconformal deformations are important. Quasiconformal
deformations are kinds of stretching and bending that do not change the angles
too much. Because of this characteristic, they have the convenient properties ofdifferentiability almost everywhere, absolute continuity and no overly-largechanges in their conformal invariants. However, this feature makes it difficult todetermine intuitively whether a given deformation is quasiconformal or not.

References（1）H. Fujino, “The existence of quasiconformal homeomorphism between planes withcountable marked points,” Kodai Math. J. 38. 732-746 (2015).
(2) H. Fujino, “Quasisymmetric embedding of the integer set and its quasiconformal
extension,” Ann. Acad. Sci. Finn. Math. 42, 575-584 (2017).

March 2019 | IAR LETTER | 12

Shingo KAZAMA

Research Highlights _ 07

Direct Dark Matter Search With XENON

Teppei KITAHARA

Research Highlights _ 08

Searching for New Physics throughPrecision Flavor Physics

Shingo KAZAMA

Teppei KITAHARA

Designated Assistant Professor of Young Leaders Cultivation Program
Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University
E-mail: kazama@isee.nagoya-u.ac.jp

Designated Assistant Professor of Young Leaders Cultivation Program
Kobayashi-Maskawa Institute / Institute for Advanced Research, Nagoya University
E-mail: teppeik@kmi.nagoya-u.ac.jp

INDIRECT EVIDENCE FOR DARK MATTER
Everything we can observe on the Earth consists of ordinary matter.
However, astronomical and cosmological observations at various scales strongly
indicate that there must exist another kind of matter in the Universe. It is notcomposed of particles that we know of so far and does not emit any radiation.
Therefore, we cannot directly observe it, and it has thus been named “darkmatter.” Nevertheless, dark matter particles have a finite mass and form large
structures in the Universe. We can observe the gravitational effects of dark matterin the dynamics of galaxies and galaxy clusters, as well as in gravitational lensing
measurements. Observation of the cosmic microwave background suggests that
there should be about five times more dark matter than ordinary matter. Despite
the huge amount of dark matter, we still do not know what it is made of. One of
the most promising theories, supersymmetry (SUSY), suggests that dark matter
consists of weakly interacting massive particles (WIMPs), which have masses
comparable to atomic nuclei. Such particles could have a non-zero interaction
cross-section with ordinary matter. Since dark matter is believed to exist
everywhere throughout our galaxy and constantly pass through the Earth, we canobserve such interactions in detectors specifically designed to identify the natureof dark matter.

particle with a xenon nucleus. The goal of the experiment is to achieve asensitivity to very small cross sections predicted by the cosmologicalobservations and theories beyond the Standard Model of particle physics such
as SUSY. The current detector, XENON1T [1], has been installed
underground at the Laboratori Nazionali del Gran Sasso (LNGS) in Italy (seeFigure 1). XENON1T, with its 3.6 tons of xenon, of which two tons are in
the active part of the detector, allowed the sensitivity to be lowered to levels
never explored so far (see Figure 2), becoming the most sensitive detector in
the world for dark matter hunting [2, 3]. This success has been made possible
thanks to the significant care put into efficiently reducing most of the sourcesof background noise that could mimic a dark matter signal, including thosethat may be produced by the detector itself.

FUTURE PROSPECTS FOR DARK MATTER SEARCH
The next phase of the XENON project, called XENONnT, foresees an
upgrade of the current detector with the aim of extending the sensitivity ofthe experiment by a factor of 10. Such a performance can be realized byincreasing the size of the target medium (to around 8.4 tons of xenon) and astronger reduction of the background. The main contribution of our groupconsists of the construction of a purification system for liquid xenon, vetosystems for the neutron background and analysis of the acquired data. Thesesystems will play important roles in achieving the designed sensitivity (seeFigure 2), and the construction of these systems is now underway to start
operation in 2019.

CP VIOLATION

Have you ever heard of “CP violation”? Some readers may have heard
this phrase ten years ago. Makoto Kobayashi and Toshihide Maskawa wereawarde d the Nobel Prize in Physics in 2008 for establishing the
Kobayashi-Maskawa theory: They discovered the origin of a violation of CP
symmetry (CP violation) and predicted the 3rd generation of quarks. This
theory has been confirmed in many different Hadron-Collider experiments
and B-factory experiments. Eventually, this theory became one of the mostimportant pieces of the Standard Model in particle physics.
The figure shows CP symmetry in particle physics as a combination of
two different types of symmetry; charge conjugation (C) symmetry and parity(P) symmetry. CP symmetry roughly corresponds to matter-antimatter
symmetry. A violation of CP symmetry, therefore, produces matter-antimatterasymmetry. CP violation plays an important role in our world; for instance,
unlike matter, anti-matter is very rare.

BEYOND THE STANDARD MODELThe Standard Model of particle physics is known to be incomplete in
the light of cosmological observations: deficits of dark matter component andin matter-antimatter asymmetry. An extension of the Standard Model istherefore essential.
One main strategy for probing physics beyond the Standard Model isprecision measurements of the properties of Standard Model particles, which
can reveal new physics contributions through radiative corrections. These
measurements often have the potential to explore new physics beyond thereach of the Large Hadron Collider.

FLAVOR PHYSICS

Figure 1: XENON1T facility in the underground hall of Laboratori Nazionali delGran Sasso (LNGS). The building on the right houses various auxiliary
systems. The cryostat containing the liquid xenon is located inside the large
water tank on the left, next to the building. (Credit: Roberto Corrieri and Patrick
De Perio)

SEARCH FOR DARK MATTER WITH LIQUID XENONThe XENON experiment is a program for the direct detection of dark
matter that uses liquid xenon as a detector medium. XENON collaboration
involves nearly 170 researchers from the Japan, the US, Germany, Italy,
Switzerland, Portugal, France, the Netherlands, Israel, Sweden and the United
Arab Emirates. The XENON experiment aims at detecting the tiny amountof charge and light that is emitted after the interaction of a dark matter
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Figure 2: Constraint on the interaction cross-section between dark matterparticles and nuclei from the XENON1T experiment. Expected sensitivity of the
XENONnT experiment is also shown.

In particle physics, the term “flavor” is used to describe species of quarks
and leptons. The Standard Model contains six flavors of quarks: up (u), down(d), strange (s), charm (c ), bottom (b) and top (t) quarks. Precision
measurement of the flavor-changing processes is called flavor physics. Flavor
physics, especially utilizing CP violation and/or flavor-changing neutral
currents, is remarkably useful in the search for new physics. The former
involves precisely comparing the decay contents of antimatter to those ofmatter. The latter represents flavor-changing processes that keep theirelectromagnetic charges, like b→s, t→c, and s→d. CP-violating processes andflavor-changing neutral currents are strongly suppressed in the Standard
Model, but they are not suppressed in new physics scenarios in general.
Therefore, their precision measurements are particularly promising in the
search for new physics.

References

KAON PHYSICS（1）E. Aprile et al., The XENON1T Dark Matter Experiment, Eur. Phys. J. C (2017)
77: 881, 2017.
（2）E. Aprile et al., First Dark Matter Search Results from the XENON1T Experiment,
Phys. Rev. Lett. 119, 181301, 2017.
（3）E. Aprile et al., Dark Matter Search Results from a One Ton-Year Exposure of
XENON1T, Phys. Rev. Lett. 121, 111302, 2018.

kaon KS). Applying this feature, the first CP violation was discovered in KL→
ππ decay in 1964. Even today, this measurement gives one of the best
sensitivity to new physics at high-energy scales.
A direct CP violation in the KL→ππ decay, represented by ε’, which isdifferent observable from discovered one in 1964, has attracted attention after
the first lattice QCD calculation was conducted in 2015. High theoreticalprecision in the Standard Model is crucial for probing the footprints of new
physics. In Ref. [1], we improved the Standard Model prediction of ε’ andconcluded that the prediction is 2.8σ below the experimental data. We also
found that this discrepancy can be explained naturally in the minimal
supersymmetric model that is one of the promising new physics scenarios.
Other interesting channels in kaon rare decays are KS→μ+μ- and KL→ π0
νν−. In Ref. [2], we discovered that a new CP violation could be observed in
KS→μ+μ- decay. KL→π0νν− emerges from a pure CP-violating contribution.
Once these channels are observed, their measurements help to search for new
physics in the future [3].

A quark and an antiquark bound together form what is called a meson.
A s quark and a light quark (u or d) bound together are called a kaon (or Kmeson). The kaon possesses an interesting feature: the neutral kaon and theanti-neutral kaon oscillate between each other, and their linear combinations
produce two different physical states (a long-lived kaon KL and a short-lived

Figure: Image of the CP transformation. The charge conjugation transformation
reverses the particle’ s charge. The parity transformation corresponds to amirror reflection. The CP transformation is their combination.

B PHYSICS

Precision measurements of B-meson decays are also very important for
probing new physics. Many physicists are continuing their great efforts. We
improved one of the Standard Model predictions for B-meson semileptonic
decays [4]. It is expected that the Belle II experiment at KEK, which is designed
to achieve a world-record collider luminosity, will bring enormous andremarkable achievements in the near future.
References（1）Kitahara T., Nierste U., Tremper P., Supersymmetric explanation of CP violation in
K→ππ decays. Phys. Rev. Lett. 117, no. 9, 091802 (2016); Singularity-free next-to-leading
order ΔS=1 RGE and ε’/ε in the Standard Model and beyond. JHEP. 1612, 078 (2016).
(2) D’Ambrosio G., Kitahara T., Direct CP violation in K→μ+μ-. Phys. Rev. Lett. 119, no.
20, 201802 (2017).
(3) Endo M., G oto T., Kita hara T., Mish ima S., Ue da D., Yamamoto K .,Gluino-mediated electroweak penguin with flavor-violating trilinear couplings. JHEP.
1804, 019 (2018).
(4) de Boer S., Kitahara T., Nisandzic I., Soft-photon corrections to B→Dτ-ν relative to B
→Dμ-ν. Phys. Rev. Lett. 120, no. 26, 261804 (2018).

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