1. Stellar cooling anomalies: hints, interpretations and experimental potential
Maurizio Giannotti,
Barry University
7th General IAXO Collaboration Meeting DESY, July 3, 2017

2. Facts and important questions
We live in a peculiar age for ALPs and astrophysics, when stellar evolution and experiments have a remarkable equivalent potential in probing ALPs.
Not only astrophysics may help understand the physics of ALPs, but ALP experiment may help understand some aspects of stellar evolution.
There is evidence of Cooling anomalies! Is this a hint to new physics? If so, which are the most likely candidates and what is the discovery potential of next generation experiments?

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

4. Stars as Laboratories
Neutrino magnetic moment (mn)
Axion-electron coupling (gae)
Hidden Photons
minicharged fermions
Hidden Photons
Extradimensions
Axion-photon coupling (gag)
Neutrino magnetic moment (mn)
Axion-electron coupling (gae)
Axion-photon coupling (gag)
G. Raffelt, “Stars as laboratories for fundamental physics” (1996)

5. Cooling Anomalies gae μ gae ; μ ga gaN Observable Stellar system
Significance
Solutions
comments
rate of period change 𝑃 /𝑃
of WD variables
G117-B15A
4 σ
gae μ
May depends on some uncertain assumptions on the oscillating modes
R548
2 σ
L19-2 (113)
1.5 σ
L19-2 (192)
0.4 σ PG
1.1 σ
Shape of WDLF WD
2.3 σ
Based on axion solution in Bertolami et. al., JCAP 1410 (2014)
Lum. RGB-tip
Globular cluster M5
1.24 σ
gae ; μ
Globular cluster -Centauri σ
Approximate estimate based on the data presented
HB stars (R=NHB/NRGB)
Globular cluster
ga
Y from Aver et. al. (2013); gae=0
Supergiants (B/R)
Open Clusters ??
Systematics in the modeling are largely unknown NS
CAS A
gaN

6. Cooling Anomalies
Practically every stellar system seems to be cooling faster than predicted by the models.
Ayala et. al. (2014), Straniero (proc. of XI 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)
M.G., Irastorza, Redondo, Ringwald (2015); M.G., Irastorza, Redondo, Ringwald (in preparation)

7. Stars as ALPs Laboratories
What can we learn about axions and ALPs from stellar evolution?
If light enough, axions-ALPs can be created in the stellar core
and then escape, carrying energy away and therefore contributing to the stellar cooling.
There are many observables which can be used to constrain them

8. Stars as ALPs Laboratories
Observable
Process
Luminosity of the RGB tip
Electron Bremsstrahlung
RGB Luminosity Function
Luminosity of the ZAHB
WD Luminosity Function
WD pulsation
RR-Lyrae pulsation
R=NHB/NRGB
Compton+Primakoff/Bremsstrahlung
R2=NAGB/NHB
SNIa rate
NS cooling
CCSN
Nuclear Bremsstrahlung

9. White Dwarf Variables
Luminosity changes periodically with a slowly increasing period.
There are several known pulsating WD, in at least 7 different classes.
The physics of these stars is relatively simple and well understood. However, observations are very recent. Also, measuring the period change well requires 2-3 decades of observations.
The quantitative analysis of the period change is quite recent
DBV
DAV
A. Corsico, Terceras Jornadas de Astrofisica Estelar (2017)

10. White Dwarf Variables
Luminosity changes periodically with a slowly increasing period.
We expected an unparalleled progress in the asteroseismic study of the origin
and evolution of WDs in
the coming years, thanks to space missions such as
TESS (Transiting Exoplanet Survey Satellite,
A. Corsico, Terceras Jornadas de Astrofisica Estelar (2017)
DBV
DAV
A. Corsico, Terceras Jornadas de Astrofisica Estelar (2017)

11. Additional cooling source:
White Dwarf Variables
Luminosity changes periodically with a slowly increasing period.
𝑃 /𝑃 is practically proportional to the cooling rate 𝑇 /𝑇
Additional cooling source:
𝑇 /𝑇
𝑃 /𝑃
DBV
DAV

12. White Dwarf Variables Observations:
Observations and models show some discrepancy
References:
Corsico et. al., Mon. Not. R. Astron. Soc. 424, 2792–2799 (2012)
Corsico et. al., JCAP 1212 (2012).
Battich et. al., (2016)
Corsico et. al., (2016)

13. White Dwarf Variables Observations:
Observations and models show some discrepancy
In addition, the hot WD shows 𝑃 /𝑃 about 2-3 orders of magnitude smaller than expected! This is difficult to explain in terms of extra-cooling!
The measurement data may still be too little for a definite conclusion
Hermes et al. (2013)
A. Corsico, private communication

14. White Dwarf Variables Observations: Neutrino magnetic moment:
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)
A non-zero μ could explain individually the hints from the WDV but not the DA and DB simultaneously, because of the temperature difference between them and of the strong temperature dependence of the μ induced rate.
A minicharged neutrino would suffer the same problem.

15. White Dwarf Variables Observations: Hidden Photons:
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)
Hidden Photons:
HP could explain the additional cooling for certain values of mass and coupling.
Sun and HB exclude most of the hinted region.

16. White Dwarf Variables Observations: ALP solution:
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)

17. White Dwarf Variables Observations: ALP solution:
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)
2s hint for a26 >0,
best fit: a26 = 0.66
(g13 = 2.9)
c2min/d.o.f. = 1.1

18. White Dwarfs Luminosity Function
Sensitive to WD cooling efficiency
χ 2 /𝑑𝑜𝑓=6
Lx= anomalous cooling, e.g. axions
The fit is not accurate, especially in the colder section.
Several systematics are not well understood and errors have been enlarged by hand
observed
expected
Data from: M. Bertolami et. al. (2014)

19. White Dwarfs Luminosity Function
The WDLF offers a unique way to test the functional dependence of the additional cooling rather than just its amplitude.
The addition of axions coupled to electrons showed improvement of the fits.
The addition of an anomalous neutrino magnetic moment showed no improvement.
Cold.
n cooling unimportant.
Linear behavior (Mestel Law). Small uncertainties
Hot;
n cooling becomes important. Nonlinear behavior.
Large uncertainties
M. Bertolami et. al. (2014)

20. WDLF and new physics A study of the WDLF in the linear region, where
was used to test emission rates of the form
The result shows a preference for rates with n=3-4, expected from electron bremsstrahlung production of axions, or for HP
Neutrinos with an anomalous magnetic moment would have n~8 and so are very inefficient 1s 2 3 4
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)

21. WDLF and new physics A study of the WDLF in the linear region, where
was used to test emission rates of the form
The HP solution is mostly excluded by the sun and HB 1s 2 3 4
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)

22. RG Cooling
A particularly useful observable in the CMD is the brightness of the tip of the RG branch.
Additional cooling would give rise to a brighter RGB tip.
Recent papers showed a tip slightly more luminous than expected
M5: (analysis of gae and mn)
Viaux et. al., Phys.Rev.Lett. 111 (2013);
Viaux et. al. Astron.Astrophys. 558
(2013) A12;
-Centauri: (analysis of mn)
Arceo-Daz et. al. (2015)
Preliminary analysis of M3 doesn’t show this anomaly.

23. RG Cooling
A particularly useful observable in the CMD is the brightness of the tip of the RG branch.
Additional cooling would give rise to a brighter RGB tip.
Recent papers showed a tip slightly more luminous than expected
M5: (analysis of gae and mn)
Viaux et. al., Phys.Rev.Lett. 111 (2013);
Viaux et. al. Astron.Astrophys. 558
(2013) A12;
-Centauri: (analysis of mn)
Arceo-Daz et. al. (2015)
A study of many more clusters is underway… O. Straniero et al., in preparation

24. RG Cooling It can be explained by
Using only the published results, the brighter than expected tip of the RG branch hints to possible new physics as shown
New cooling channel
It can be explained by
Neutrino magnetic moment: μ  2 x 10-12μB
Axion-electron coupling HP
Viaux et. al., Phys.Rev.Lett. 111 (2013);
Viaux et. al., Astron.Astrophys. 558 (2013) A12

25. RG Cooling
The brighter than expected tip of the RG branch hints to additional cooling.
Viaux et. al., Phys.Rev.Lett. 111 (2013)
Viaux et. al. Astron.Astrophys. 558 (2013)
Neutrino magnetic moment: μ  2 x 10-12μB
Axion-electron coupling
gae  2 x 10-13
Hidden photons
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)

26. RG Cooling Another observable is the brightness of the ZAHB.
Additional cooling would increase the core mass at the beginning of the HB which in turn would increase the luminosity
Preliminary analysis in this case shows a mild preference for an axion electron coupling

27. Summary: ALP-electron coupling
ALPs coupled to electrons can explain all the WD+RGB hints reasonably well
1-parameter fit
Combined
Analysis:
3s hint for a26 > 0
best fit: a26 = 0.18,
(g13 = 1.5)
c2min/d.o.f. = 1.15
M.G., Irastorza, Redondo, Ringwald, K. Saikawad, (in preparation)

28. The R-parameter R=NHB/NRG The R-parameter:
compares the number of stars in the HB (NHB) and in the upper portion of the RGB (NRG).
Straniero (proc. of XI Patras Workshop)
Ayala, Dominguez, M.G., Mirizzi, Straniero, PRL (2014)
Assuming Gaussian errors, the observed and measured values of R are 2 apart.
However, more recent analysis seems to soften this discrepancy.

29. Testing gae and ga R=NHB/NRG a e g Ze
RGB: Very dense. Sensitive to gae g
gag Ze a
HB: Not very dense. Sensitive to gag
M.G., Irastorza, Redondo, Ringwald (2015)
Straniero, Dominguez, M.G., Mirizzi, in preparation

30. The R-parameter: HP
The current results can be explained by Hidden Photons and ALPs
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)

31. The R-parameter: ALPs HB-Hint
The current results can be explained by Hidden Photons and ALPs
ALP CDM
QCD axion band
Transparency
hints
CIBER
SN 1987A
NGC 1275
HB-Hint
Assume a negligible ALP-electron coupling

32. Putting all together:  and HP
Neutrinos with anomalous electromagnetic factors cannot explain the WDLF or the pulsation results or DA and DB variable at the same time, since the temperature dependence of the emission rate is too steep.
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)
Hidden photons could explain all the different hints independently but there is no overlap of the regions hinted by the different anomalies.
excluded
hint
excluded
hint
excluded
hint

33. Putting all together: ALPs
NOTICE, ALPs coupled to electrons can also explain the R-parameter hint!
M.G., I. Irastorza, J. Redondo, A. Ringwald, JCAP 1605 (2016)
1-parameter fit
Combined
Analysis:
3s hint for a26 > 0
best fit: a26 = 0.18,
(g13 = 1.5)
c2min/d.o.f. = 0.96
M.G., Irastorza, Redondo, Ringwald, K. Saikawad, (in preparation)

34. Putting all together: ALPs
However, with the currently published analysis there is a preference for a small coupling to photons too
best fit:
c2min/d.o.f. = 1.14
best fit corresponds to:
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation

35. KSVZ axion In the KSVZ model, coupling to electrons naturally small
best fit corresponds to: g
gag e a
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation
In fact, too small!
So, c2min/d.o.f. > 2

36. SMASH axion
In the SMASH model, the one-loop induced axion-electron coupling gets extra contributions from neutrinos
best fit corresponds to:
In this case the fit is considerably improved
c2min/d.o.f. = 1.1
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation

37. NS in CAS-A
Measured surface temperature over 10 years of the NS in Cas A reveals unusually fast cooling rate.
The thermal energy losses are approximately twice more efficient than it can be explained by the neutrino emission. [Shternin et. al., Mon. Not. R. Astron. Soc. 412 (2011)]
expected
observed
χ 2 /𝑑𝑜𝑓=4
Leinson, JCAP 1408 (2014)

38. NS in CAS-A
Measured surface temperature over 10 years of the NS in Cas A reveals unusually fast cooling rate.
The thermal energy losses are approximately twice more efficient than it can be explained by the neutrino emission. [Shternin et. al., Mon. Not. R. Astron. Soc. 412 (2011)]
expected
observed
The observations could also be explained by an ALP coupled to nucleons [Leinson, JCAP 1408 (2014)] but the effect could have a different origin, for example as a phase transition of the neutron condensate into a multicomponent state [Leinson, Phys. Lett. B 741, (2015)]
χ 2 /𝑑𝑜𝑓=4
Leinson, JCAP 1408 (2014)

39. Anomaly in the cooling of NS
The additional cooling could be explained by introducing an ALP produced through nucleon bremsstrahlung.
g 𝑎𝑛 = 3.8±3 × 10 −10
[Leinson, JCAP 1408 (2014)],
compatible with upper limits from NS cooling
g 𝑎𝑛 ≤8× 10 −10
[J. Keller and A. Sedrakian, Nucl. Phys. A897, 62 (2013);
A. Sedrakian, Phys.Rev. D93 (2016) ]
The effect could have a different origin, for example as a phase transition of the neutron condensate into a multicomponent state [Leinson, Phys. Lett. B 741, (2015)]
Leinson, JCAP 1408 (2014)

40. Bound from Supernova 1987A
Assuming that theSN1987A neutrino burst was not shortened by more than ~½ leads to an approximate requirement on a novel energy-loss rate of
ex<1019erg g-1 s-1
for r ≈3×1014g cm-3 and T≈30 MeV a
gaN N
This leads to:
Compatible with the NS hint.
However, not a very solid bound: very few data and the interaction is difficult to model.
Fischer, Chakraborty, M. G., Mirizzi, Payez, Ringwald, (2016)

41. IAXO Detection Potential
IAXO has the potential of exploring very interesting regions of the axion parameter space
CAST
ALPS II
SN 87A
HB-Hint
IAXO
IAXO+
Fermi LAT
QCD axions
IAXO collaboration, in preparation

42. IAXO Detection Potential
IAXO has the potential of exploring very interesting regions of the axion parameter space
CAST
ALPS II
SN 87A
HB-Hint
IAXO
IAXO+
SN87A
Fermi LAT
QCD axions
IAXO collaboration, in preparation

43. IAXO Detection Potential
CAST
IAXO
IAXO+
ALPS II
SN 87A
Fermi LAT
HB-Hint
DFSZ 1
DFSZ 2
KSVZ
SMASH
NGC1275
The KSVZ/SMASH region is built as 1 bands for fixed E/N.
values of the 2min are fairly high with respect to the DFSZ model
M.G., Irastorza, Redondo, Ringwald, K. Saikawad, In preparation

44. IAXO Detection Potential
CAST
IAXO
IAXO+
ALPS II
SN 87A
Fermi LAT
HB-Hint
DFSZ 1
DFSZ 2
NGC1275
KSVZ
SMASH
The SN 1987A bound cuts a large part of the area accessible to IAXO, but should probably not be considered as a sharp bound
SN87A
Fischer, Chakraborty, M. G., Mirizzi, Payez, Ringwald, (2016)
M.G., Irastorza, Redondo, Ringwald, K. Saikawad, In preparation

45. IAXO Detection Potential: DFSZ
DFSZ Axions:
Tree-level interactions with electrons.
Two DFSZ models, depending on which Higgs gives mass to charged leptons.
DFSZ 1:
𝐶 𝑒 = Cos 2 ⁢𝛽 3 ; 𝐶 aγ = 8 3 −1.92
DFSZ 2:
𝐶 𝑒 = Sin 2 ⁢𝛽 3 ; 𝐶 aγ = 2 3 −1.92
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation

46. IAXO Detection Potential: DFSZ
DFSZ Axions:
Tree-level interactions with electrons.
Two DFSZ models, depending on which Higgs gives mass to charged leptons.
DFSZ 1:
SN87A
𝐶 𝑒 = Cos 2 ⁢𝛽 3 ; 𝐶 aγ = 8 3 −1.92
DFSZ 2:
𝐶 𝑒 = Sin 2 ⁢𝛽 3 ; 𝐶 aγ = 2 3 −1.92
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation

47. Detection Potential: DFSZ 1
ma [eV]
Hints:
HB, RGB stars and WDs
Hints:
HB, RGB stars and WDs +
NS in Cassiopeia A and the bound from SN 1987A
M.G., Irastorza, Redondo, Ringwald, K. Saikawad, In preparation

48. Detection Potential: DFSZ 2
fa [GeV]
fa [GeV]
Hints:
HB, RGB stars and WDs
Hints:
HB, RGB stars and WDs +
NS in Cassiopeia A and the bound from SN 1987A
M.G., Irastorza, Redondo, Ringwald, K. Saikawad, In preparation

49. Detection Potential: hadronic SMASH
1, 2, and 3  intervals for SMASH axions (WD+RG+R-parameter)
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation
In all cases, c2min/d.o.f. = 1.14

50. Detection Potential: hadronic SMASH
1, 2, and 3  intervals for SMASH axions (include SN and NS from CAS A)
ARIADNE
ARIADNE
ARIADNE
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation

51. Detection Potential: KSVZ and DFSZ
Fits include HB, RGB, WD pulsation, WDLF
Model
E/N
tan 
fa [106 GeV]
ma [meV]
2/dof
KSVZ -- 77 74
2.36
2/3 50
110
5/3
8.0
710
2.21
8/3
2.6
220
2.19
SMASH 53
1.14 22
260 64 89
DFSZ I
0.25 63
DFSZ II
3.1
107
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation

52. Detection Potential: KSVZ and DFSZ
Fits include HB, RGB, WD pulsation, WDLF
Model
E/N
tan 
fa [106 GeV]
ma [meV]
2/dof
KSVZ -- 77 74
2.36
2/3 50
110
5/3
8.0
710
2.21
8/3
2.6
220
2.19
SMASH 53
1.14 22
260 64 89
DFSZ I
0.25 63
DFSZ II
3.1
107
M.G., I. Irastorza, J. Redondo, A. Ringwald, K. Saikawad, In preparation
For the DFSZ axion, adding the results from SN and NS, the mass drops by a factor of about 10 and the 2/dof moves to about 1.6

53. Conclusion
new observations  new observables could be used to study the impact of new physics on stellar evolution and to remove some degeneracies.
A dedicated research program could improve considerably the current status of understanding.
Currently, we observe hints from several stellar systems. ALPs and DFSZ axions are the best candidates to explain. KSVZ is not as good. SMASH is also a good candidate
IAXO has strong detection potential for axion and ALPs. The combination of IAXO and ARIADNE could probe the hinted parameter space, especially for the DFSZ case.

54. the evolution of stellar evolution
Follow-up:
the evolution of stellar evolution
There are other issues with stellar evolution which need to be addressed:
There is a long standing issue with the discrepancy between the predicted and observed SN type Ia rate. Axions would increase this rate since they would move the threshold for stars to become SN type II.
We know the result of the stellar pulsation of only a handful of pulsators out of over 100 know. This situation may change soon.
Analysis are often based on partial results that are old. There is data that has not yet been properly analyzed
We need a serious effort in the stellar evolution community directed toward the study of new physics.
IAXO, probing the area of g11 below a few, will help shed light also on stellar evolution

55. The discrepancy between the predicted and observed SNIa rate is one of the key problems still open in SNIa. I would say that has worsen in recent years when more observations became available.
The two scenarios, in the "classical" model for SNIa (thermonuclear explosion of a CO WDs near-Chandrasekhar mass) are the double degenerate (merging of 2 WDs) and the single degenerate (WD accreting from a "normal" star). None of them (via population synthesis codes) reproduce the observed rates and even less what is called the observed "Delayed Time Distributions (DDT)" of SNIa, this is SNIa rate in function of the "age of the galaxies/populations in which they occur" (theoretically the time since the formation of the SNIa progenitor systems, star formation, to the explosion time).
I attached a plot from a Review by Maoz et al. 2014, the DD are bellow the expectations and the SD (depending on the group) are bellow by 2-3 order of magnitudes ()
This is the main reason of the "revival" of sub-Chandrasekhar (also called double detonations or He-detonations): if all mergers of 2 CO WDs explode the estimated rate would be OK.
In summary, increasing the number of "massive" CO WDs is always "welcome". Of course, we should assumed and IMF and estimate how many of them and in particular also their masses... uhmmm, now I think it's not so clear, we increase the number of stars contributing to the CO WDs (and this is in the "good" direction) but if the more massive WDs comes from massive progenitors, their number may decrease ... depends on the IMF !!
All what is said above about rates and DDT, from the observational and from the theoretical point of view has many uncertainties ! (but the discrepancy is "big")