Stellar evolution andaxions
Maurizio Giannotti,
Barry University

International workshop on Axion physics and dark
matter cosmology
Osaka University, December 20, 2017

Stars as ALPs Laboratories
What can we learn about axions/ALPs from stars?
Pioneered in M. Fukugita, S. Watamura, and M. Yoshimura, Phys. Rev. Lett. 48,
1522 and M. Fukugita, S. Watamura, and M. Yoshimura, Phys. Rev. D 26, 1840

Stars as ALPs Laboratories
What can we learn about axions/ALPs from stars?

If light enough, axions-ALPs can be created in the stellar core

… and escape the star, contributing to the cooling!

Stars as Laboratories

G. Raffelt, “Stars as laboratories for fundamental physics” (1996)

White Dwarf Variables
Luminosity changes periodically with aslowly changing period.

𝑃/𝑃 is practically proportional
to the cooling rate 𝑇/𝑇

Additional coolingsource:
𝑇/𝑇
DBV

DAV

A. Corsico, Terceras Jornadas de Astrofisica Estelar (2017)

𝑃/𝑃

White Dwarf Variables
Observations and models show some discrepancy

M.G., I. Irastorza, J. Redondo,
A. Ringwald, JCAP 1605 (2016)-- Theory-- Observations

M.G., I. Irastorza, J. Redondo,
A. Ringwald, K. Saikawa, JCAP1710 (2017)

The discrepancies run
from 0.4 to 4 2 hint for 26 >0,
best fit: 26 = 0.66 (g13 = 2.9)
2min/d.o.f. = 1.1
bound (2): 26 < 1.3 (g13 <4.1)

White Dwarfs Luminosity Function
White Dwarfs Luminosity Function:

Sensitive to WD coolingefficiency

dNWD
1

dV dL L  L  Lx

χ2 /𝑑𝑜𝑓 = 6

Lx= anomalous cooling, e.g.
axionsobserved
expected

Data from: M. Bertolami et. al. (2014)

The fit is not accurate,
especially in the colder
section.
Several systematics are notwell understood and errors
have been enlarged by handWhite Dwarfs Luminosity Function
White Dwarfs Luminosity Function:

ALPs analysis(1-parameter, 11 points)

χ2 /𝑑𝑜𝑓 = 6observed
expected

Best fit value: g13=1.4
Bound (2): g13<2.1

Data from: M. Bertolami et. al. (2014)

2min/d.o.f. = 0.94

RG Cooling
A particularly useful observable is the brightness of the tip of the RG
branch.

Additional cooling would giverise to a brighter RGB tip.

aeZegaeZeeRG Cooling
A particularly useful observable is the brightness of the tip of the RG
branch.

Additional cooling would give rise to a brighter RGB tip.
Cluster

Results

M5: (analysis of gae and µν)Shows a slightly brighter tip

-Centauri: (analysis of µν)

Shows a slightly brighter tip

M3: (analysis of gae)

Compatible with observations

Viaux et. al., Phys.Rev.Lett. 111 (2013);
Viaux et. al. Astron.Astrophys. 558(2013) A12;

Arceo-Daz et. al. (2015)

O. Straniero et. al. (2017)

RG Cooling
A particularly useful observable is the brightness of the tip of the RG
branch.

Additional cooling would give rise to a brighter RGB tip.

Likelihood

Combined analysis M3+M5

M5
M5
M3
M3

A study of many more clusters isunderway…

Best fit value: g13=1.4
Bound (2): g13<3.1

HB stars and the R-parameter
R=NHB/NRGae
Ze

RGB: Very dense.
Sensitive to gae

gaee

Zea

Zega



Ze

HB: Not very dense.
Sensitive to ga

Ayala, Dominguez, M.G., Mirizzi,Straniero, (2014)
Straniero (proc. of XI PatrasWorkshop, 2015)
M.G., Irastorza, Redondo,Ringwald (2015)

HB stars and the R-parameter
R=NHB/NRG2

1

Ayala, Dominguez, M.G., Mirizzi,
Straniero, (2014)
M.G., Irastorza, Redondo, Ringwald, JCAP 1605 (2016)

Straniero (proc. of XI Patras
Workshop, 2015)
M.G., Irastorza, Redondo,Ringwald (2015)

Supernovae and Neutron Stars
SN and NS are very dense and much hotter than regular stars ≈a few 1014g cm-3 and T≈a few 10 MeV

ALP production: Bremsstrahlungor Primakoff.
aaNgaNNN
NZega

ZeStrong bounds from cooling considerations or from missing gamma raysfrom ALP decay/conversion in external B

Supernovae and Neutron Stars
SN and NS are very dense and much hotter than regular stars ≈a few 1014g cm-3 and T≈a few 10 MeV
Additional axion induced cooling would affect the observed
neutrino signal from SN1987A
This leads to:g ap  9  1010for KSVZ

T. Fischer, S. Chakraborty, M. G., A. Mirizzi,
A. Payez, A. Ringwald, Phys.Rev. D94 (2016)

22g ap g an 3.6 10 19for DFSZ

M.G., I. Irastorza, J. Redondo, A. Ringwald,K. Saikawa, JCAP 1710 (2017)

However, not a very solid bound: very few data and the interaction isdifficult to model. With a complete error budget, the bound should relax
Very recent “astrophobic” models could not suffer from thisbound.

Di Luzio, Mescia, Nardi,Panci, Ziegler (2017)

Hints of new physics?
As seen, several stellar systems seem to be cooling faster than
predicted by the models, perhaps hinting to new physics.
Though these hints should be taken carefully, they could show asystematic problem in our understanding of stellar evolution.

M.G., I. Irastorza, J. Redondo,A. Ringwald, JCAP 1605 (2016)
M.G., I. Irastorza, J. Redondo,
A. Ringwald, k. Saikawa, JCAP
1710 (2017)

Axions/ALPs could provide a simple explanation of all of them.
Ayala et. al. (2014); Straniero et. al. (proc. of XI Patras Workshop)
Straniero et. al. (proc. of XIII Patras Workshop)
Viaux et. al. (2013), Arceo-Daz et. al. (2015)
Bertolami (2014)

Corsico et. al., (2014, 2015); Battich et. al. (2016)
Kepler et. al., (1991) + many others
Corsico et. al., (2012)
Corsico et. al., (2016)

Corsico et. al., (2016)
Shternin et. al. (2011)

ALP/Axion interpretation
Stellar cooling shows a mild preference for a small coupling to photons
and electrons
Best fit
WDV, WDLF, RGB (M3+M5), HB

g ae  1.6  10 -13
g a  0.12  10 -10 GeV 132

1

ALPS II, TASTE,
Baby-IAXO

C
g ae  me ae
faIAXO

best fit corresponds to:M.G., I. Irastorza, J. Redondo, A. Ringwald,
K. Saikawa, JCAP 1710 (2017)g a Cae 2.7  10  2C a C a2 f a

ALP/Axion interpretation
Stellar cooling shows a mild preference for a small coupling to photons
and electrons
In the KSVZ model, coupling toelectrons naturally small

WDV, WDLF, RGB (M3+M5), HBa32

1ega



ALPS II, TASTE,
Baby-IAXO

In fact, too small!
IAXO

M.G., I. Irastorza, J. Redondo, A. Ringwald,
K. Saikawa, JCAP 1710 (2017)

Cae / Ca  10 3So, 2min/d.o.f. > 2e

ALP/Axion interpretation
Stellar cooling shows a mild preference for a small coupling to photonsand electrons
For the DFSZ I (II) model, thismeans a preference for a small(large) tan 

WDV, WDLF, RGB (M3+M5), HB3DFSZ I:21

ALPS II, TASTE,Baby-IAXO
IAXO

M.G., I. Irastorza, J. Redondo, A. Ringwald,
K. Saikawa, JCAP 1710 (2017)

Sin2 ⁢𝛽2𝐶𝑒 =;⁢𝐶aγ = − 1.92
33

Cos2 ⁢𝛽8𝐶=;⁢⁢𝐶=− 1.92
DFSZ II: 𝑒aγ
33Both DFSZ I and II explain fairly well
the combined observations
2min/d.o.f.  1

ALP/Axion interpretation
Stellar cooling shows a mild preference for a small coupling to photons
and electrons

In the KSVZ-type axi-majoron (a/J)
models, the one-loop induced axionelectron coupling gets extra
contributions from neutrinos

WDV, WDLF, RGB (M3+M5), HB32

1

ALPS II, TASTE,
Baby-IAXO
IAXO

In this case the fit can improveconsiderably2min/d.o.f.  1

M.G., I. Irastorza, J. Redondo, A. Ringwald,
K. Saikawa, JCAP 1710 (2017)

G. Ballesteros, J. Redondo, A. Ringwald and C. Tamarit,
PRL 118 (2017); JCAP 1708 (2017)

Experimental Probes
How do we probe the parameter space hinted by the cooling anomalies?

Experimental Probes
How do we probe the hinted parameter space?
The best option is in the next generation axion
helioscope IAXO

Experimental Probes
How do we probe the hinted parameter space?
The best option is in the next generation axion
helioscope IAXO
The long range force experiments.
Particularly, ARIADNE shows potential toprobe the hinted axion parameter space

From Kim, Kim, Shin, Semertzidis, Patras workshop 2016

Experimental Probes
How do we probe the hinted parameter space?
The best option is in the next generation axion
helioscope IAXO
The long range force experiments.
Particularly, ARIADNE shows potential toprobe the hinted axion parameter space

From Kim, Kim, Shin, Semertzidis, Patras workshop 2016

The hinted parameter space for very light ALPs could be probed by ALPS II
or by space-born X- and Gamma-ray detectors such as Fermi and NuSTAR

Axion Helioscope
Axion helioscope concept
P. Sikivie, 1983
+ K. van Bibber, G. Raffelt,
et al. (1989)(use of buffer gas)

•Relatively strong sensitivity•

Little dependence on the mass.

•Minimal model dependence

Slide from Igor G. Irastorza, Axion-WIMP, Thessaloniki, May 2017

Standard Primakoff
spectrumNon-hadronic “ABC” Solaraxion flux at Earth
JCAP 1312 008(only if axion couples toelectron)

X-ray Focussing &low-background
Innovations of CAST

Axion Helioscope
CAST (CERN Axion Solar Telescope).
3rd gen helioscope. Very successful inconstraining the axion-photon coupling fora wide mass range.

CAST coll., Nature Phys. 13 (2017) 584-590

IAXO: The International Axion Observatory
4th generation axion helioscopeInternational proposal for a 4th generation
axion helioscope

IAXO: The International Axion Observatory
4th generation axion helioscope• Large toroidal 8-coil magnet L = ~20 m• 8 bores: 600 mm diameter each
• 8 x-ray telescopes + 8 detection systems• Rotating platform with services

IAXO: The International Axion Observatory
IAXO magnet••••

Superconducting “detector” magnet
Toroidal geometry (8 coils)
Based on ATLAS toroid technical solutions
8 bores| 20m long| 60cm ⌀ per bore|5.4/2.5 T

IAXO telescopes•••

Slumped glass technology with multilayers
Cost-effective to cover large areas
Based on NuSTARtechnology••

Focal length ≃ 5m
8 optics with 123layers each60-70% efficiency•

IAXO detectors••

Micromegas gaseous detectors
Radiopure components+ shielding•

Event topology in gas fordiscrimination
Bgrd ≤10-7/(keV×cm2×s)
through fabrication,radiopurity, shielding andsimulations•IAXO Letter of Intent: CERN-SPSC-2013-022
IAXO Conceptual Design: JINST 9 (2014), T05002,[arXiv::1401.3233]

Improving the sensitivity
e1/ 2 10s  BL  Adetectorsopticsmagnet

b = background = efficiencys = spot size
0= efficiency

1/2 -1 g  b4ag

2

1 t

1 / 2exposure

B = magnetic fieldt = time
L = magnet length
A = cross-sectional area

IAXO is expected to improve on the CAST sensitivity to ga by a factor of 20

IAXO Letter of Intent: CERN-SPSC-2013-022;
IAXO Conceptual Design: JINST 9 (2014), T05002 [arXiv::1401.3233]

IAXO sensitivity prospects
IAXO collaboration, paper in preparation

Much larger
QCD axion
region exploredTransparency
anomaly totally
explored

Stellar coolinganomaly largely
explored

Galactic SN

Slide from Igor G. Irastorza, Axion-WIMP, Thessaloniki, May 2017

mini-IAXO (aka babyIAXO)• Goal: full intermediate experimental stage• Test magnet design at relevant scale (only
1 bore full diameter)• Test bench for optics + detector• Will deliver relevant physics (atintermediate level). Under work
• Will better mobilize community intoexperimental activity & increase interest

Detailed conceptual design
under preparation:
Presumably:
1-bore magnet with relevant
dimensions.
1 optics+detector system of specs
close to final ones.

• Better (more staged) access to funding• Detail concept and effect on near-termplanning under intense study at the momentin the collaboration.

From Igor G. Irastorza, Axion-WIMP, Thessaloniki, May 201732

Experimental Potential
Medium Size next generation Helioscopes (MSH) such as
BabyIAXO or TASTE can probe ALPs - but not easily QCD
axions – in the regions of interest for astrophysics

TASTE

Transparency hints

Galactic SN

KSVZ axion band:
Di Luzio, Mescia, Nardi,
Phys.Rev.Lett. 118 (2017),
Phys.Rev. D96 (2017)

E/N=0

IAXO collaboration, in preparation

IAXO has the greatest
potential in theregions of interest forastrophysics

Experimental Potential
Medium Size next generation Helioscopes (MSH) such as
BabyIAXO or TASTE can probe ALPs - but not easily QCD
axions – in the regions of interest for astrophysics

Cooling hints

Transparency hints

Galactic SN

KSVZ axion band:
Di Luzio, Mescia, Nardi,
Phys.Rev.Lett. 118 (2017),
Phys.Rev. D96 (2017)

E/N=0

IAXO collaboration, in preparation

IAXO has the greatest
potential in theregions of interest for
astrophysics

Experimental Potential
The low mass region can be probed extremely well with gamma and X-ray
detectors

Transparency hints

KSVZ axion band:
Di Luzio, Mescia, Nardi,
Phys.Rev.Lett. 118 (2017),
Phys.Rev. D96 (2017)

Galactic SN

M.G., Axion-WIMP, Thessaloniki, May 2017

Experimental Potential: QCD axions
Medium Size next generation Helioscopes (MSH) such as
BabyIAXO or TASTE can probe ALPs - but not easily QCD
axions – in the regions of interest for astrophysics

TASTE
Baby-IAXO

E/N=0

IAXO collaboration, in preparation

KSVZ axion band:
Di Luzio, Mescia, Nardi,
Phys.Rev.Lett. 118 (2017),
Phys.Rev. D96 (2017)

IAXO has the greatest
potential in theregions of interest for
astrophysics

Experimental Potential: DFSZ axions

From Kim, Kim, Shin, Semertzidis, Patras workshop 2016

ARIADNE searches for long range forces
mediated by axions.
The experiment would probe the coupling ofaxions to neutrons
J. E. Moody and F. Wilczek, Phys. Rev. D 30, 130 (1984).
A. Arvanitaki and A. A. Geraci, Phys. Rev. Lett. 113 (2014)

DFSZ

Most optimistic
coupling

ARIADNE can probe sections ofthe DFSZ parameter space and ismore sensitive than IAXO at lowmasses

Experimental Potential: DFSZ axions
WD, RG,HB

ARIADNE

IAXO

tan 

IAXO
ARIADNE
IAXO+

IAXO+DFSZ IItan 

DFSZ I+ SN 1987A

IAXO+
IAXO
IAXO+

ARIADNE

WD, RG,HB
ma [eV]

IAXO
ARIADNE+ SN 1987A
ma [eV]

M.G., Irastorza,
Redondo,Ringwald, Saikawa,
JCAP 1710 (2017)

Conclusion- Astrophysical bounds on axion/ALPs are improving and terrestrial
experiments are catching up! It is an exciting period!

-Hints from several stellar systems. ALPs and DFSZ axions are the best
candidates to explain the hints. Axi-majoron models are also good candidates
while KSVZ are not as good.
- IAXO will be capable to find the hinted QCD axions in a sizeable part of theparameter space, although it is with the upgraded IAXO configuration thatmost of the parameter space will be covered.
- Medium size helioscopes would likely miss the most interesting regions forDFSZ axions but could probe KSVZ and ALPs.