Astrophysical Axion Bounds

2006

Axion emission by hot and dense plasmas is a new energy-loss channel for stars. Observational consequences include a modification of the solar sound-speed profile, an increase of the solar neutrino flux, a reduction of the helium-burning lifetime of globular-cluster stars, accelerated white-dwarf cooling, and a reduction of the supernova SN 1987A neutrino burst duration. We review and update these arguments and summarize the resulting axion constraints.

Nuclear Physics B - Proceedings Supplements, 1999

If axions exist, they are copiously produced in hot and dense plasmas, carrying away energy directly from the interior of stars. Various astronomical observables constrain the operation of such anomalous stellar energy-loss channels and thus provide restrictive limits on the axion interactions with photons, nucleons, and electrons. In typical axion models a limit ma < ∼ 10 −2 eV is implied. The main arguments leading to this result are explained, including more recent work on the important supernova 1987A constraint.

Physics Letters B, 1984

We consider the contribution of bremsstrahlung emission of axions to stellar energy losses. This process has a much weaker temperature dependence than previously considered axion emission processes. It is comparable to these processes in the sun, and for objects with non-degenerate core temperatures less than 85% that of the solar core, axion bremsstrahlung will dominate. We briefly consider the implications of these axion emission losses for altering the evolution of old globular cluster stars.

Physics Reports, 1990

Prologue 3 7.1. Energy loss and energy transfer in the Sun; first 12. 1 he stellar energy loss argument 4 constraints 60 1.3. Other methods of stellar particle physics 8 7.2. Results from a germanium spectrometer 62 2. Axion phenomenology 10 7.3. A magnetic conversion experiment 62 2.1. Generic features of the Peeeei-Quinn mechanism 10 7.4. Radiative particle decays and solar-y-rays 63 2.2. The most common axion models 15 8. Red giants and horizontal branch stars 63 2.3. Fine points of axion properties (7 8.1. The general agenda 64 3. Axion cosmology 22 8.2. The evolution of low-mass stars 65 3.1. Inflationary scenario 23 8.3. Suppression of the helium flash by particle emission 68 3.2. Topological structures 24 8.4. Reduction of the helium burning phase 71 3.3. Thermally produced axions 26 8.5. Core mass at the helium flash 74 3.4. Decaying axions and a glow of the night sky 26 9. The white dwarf luminosity function 77 3.5. Experimental search for galactic axions 27 9.1. White dwarfs: theoretical and observed properties 77 4. Emission rates from stellar plasmas 28 9.2. Cooling theory for white dwarfs 79 4.1. General discussion of the emission rates 28 9.3. Neutrino losses included 81 4.2. Absorption rates 29 9.4. Axion bounds 81 4.3. Many-body effects in stellar plasmas 30 10. Cooling of nascent and young neutron stars 82 4.4. Compton process 39 10.1. Birth and cooling of neutron stars 82 4.5. Electron-positron annihilation 41 10.2. Supernova explosions and new particle physics 87 4.6. Bremsstrahlung by electrons 42 1(1.3. SN 1987A bounds on novel cooling phenomena 89 4.7. Axio-recombination and the axio-electric effect 44 10.4. Non-detection of new particles from SN 1987A 93 4.8. Bremsstrahlung by nucleons 45 10.5. SN 1987A axion bounds from numerical investiga-4.9. Primakoff effect and axion-photon mixing 49 tions 93 4.10. Plasmon decay rate 54 10.6. Axion trapping 97 .5. Energy transfer 55 10.7. Axion bounds from Einstein observations 97 5.1. Radiative transfer by massive bosons 56 10.8. What if neutron stars are strange quark stars? 98 5.2. Opacity contribution of massive pseudoscalars 56 11. Summary of axion and neutrino hounds 98 6. Exotic energy loss of low-mass stars; analytic treatment 57 11.1. Neutrinos 98 6.1. The equations of stellar structure 57 11.2. Axions 100 6.2. Homologous changes 58 References 104

Nuclear Physics A, 2013

Once formed in a supernova explosion, a neutron star cools rapidly via neutrino emission during the first 10 4 -10 5 yr of its life-time. Here we compute the axion emission rate from baryonic components of a star at temperatures below their respective critical temperatures T c for normal-superfluid phase transition. The axion production is driven by a charge neutral weak process, associated with Cooper pair breaking and recombination. The requirement that the axion cooling does not overshadow the neutrino cooling puts a lower bound on the axion decay constant f a > 6 × 10 9 T -1 c 9 GeV, with T c 9 = T c /10 9 K. This translates into a upper bound on the axion mass m a < 10 -3 T c 9 eV.

The Identification of Dark Matter - Proceedings of the Sixth International Workshop, 2007

We discuss solar signatures suggesting axion(-like) particles. The working principle of axion helioscopes can be behind unexpected solar X-ray emission, even above 3.5 keV from non-flaring active regions. Because this is associated with solar magnetic fields (~B 2 ), which become in this framework the catalyst and not the otherwise suspected / unspecified energy source of solar X-rays. In addition, the built-in fine tuning we may (not) be able to fully reconstruct, and, we may (not?) be able to copy. Solar axion signals are transient X-ray brightenings, or, continuous radiation from the corona violating the second law of thermodynamics and Planck"s law of black body radiation. To understand the corona problem and other mysteries like flares, sunspots, etc., we arrive at two exotica: a) trapped, radiatively decaying, massive axions allow a continuous self-irradiation of the Sun, explaining the sudden temperature inversion ~2000 km above the surface and b) outstreaming light axions interact with local fields (~B 2 ), depending crucially on the plasma frequency which must match the axion rest mass, explaining the otherwise unpredictable transient, but also continuous, solar phenomena. Then, the photon energy of a related phenomenon might point at the birth place of involved axions. For example, this suggests that the ~2 MK solar corona has its axion roots at the top of the radiative zone. The predicted B ≈ 10-50 T make this place a coherent axion source, while the multiple photon scattering enhances the photon-to-axion conversion unilaterally, since axions escape. We conclude that the energy range below some 100 eV is a window of opportunity for axion searches, and that it coincides with a) the derived photon energies for an external self-irradiation of the Sun, which has to penetrate until the transition region, and b) with the bulk of the soft solar X-ray luminosity of unknown origin. Thus, (in)direct signatures support axions or the like as an explanation of enigmatic behavior in the Sun and beyond; e.g., the otherwise unexplained "solar oxygen crisis" taking into account related observations (~B 2 ) in pores, which is associated with X-ray emission. Axion antennas could take advantage of such a feed back. Finally, the observed soft X-ray emission from the quiet Sun at highest latitudes as well as the extended activity associated with magnetic structures crossing the solar disk centre suggest that a multicomponent axion(-like) scenario is at work.

Physical review, 2016

We study the impact of axion emission in simulations of massive star explosions, as an additional source of energy loss complementary to the standard neutrino emission. The inclusion of this channel shortens the cooling time of the nascent protoneutron star and hence the duration of the neutrino signal. We treat the axion-matter coupling strength as a free parameter to study its impact on the protoneutron star evolution as well as on the neutrino signal. We furthermore analyze the observability of the enhanced cooling in current and next-generation underground neutrino detectors, showing that values of the axion mass ma 8 × 10 −3 eV can be probed. Therefore a galactic supernova neutrino observation would provide a valuable possibility to probe axion masses in a range within reach of the planned helioscope experiment, the International Axion Observatory (IAXO).

Physical Review Letters, 2005

Journal of Cosmology and Astroparticle Physics, 2021

It has been recently claimed by two different groups that the spectral modulation observed in gamma rays from Galactic pulsars and supernova remnants can be due to conversion of photons into ultra-light axion-like-particles (ALPs) in large-scale Galactic magnetic fields. While we show the required best-fit photon-ALP coupling, gaγ ∼ 2 × 10-10 GeV-1, to be consistent with constraints from observations of photon-ALPs mixing in vacuum, this is in conflict with other bounds, specifically from the CAST solar axion limit, from the helium-burning lifetime in globular clusters, and from the non-observations of gamma rays in coincidence with SN 1987A. In order to reconcile these different results, we propose that environmental effects in matter would suppress the ALP production in dense astrophysical plasma, allowing to relax previous bounds and make them compatible with photon-ALP conversions in the low-density Galactic medium. If this explanation is correct, the claimed ALP signal would b...

Physics Letters B, 2002

We have recently proposed a mechanism of photon-axion oscillations as a way of rendering supernovae dimmer without cosmic acceleration. Subsequently, it has been argued that the intergalactic plasma may interfere adversely with this mechanism by rendering the oscillations energy dependent. Here we show that this energy dependence is extremely sensitive to the precise value of the free electron density in the Universe. Decreasing the electron density by only a factor of 4 is already sufficient to bring the energy dependence within the experimental bounds. Models of the intergalactic medium show that for redshifts z < 1 about 97% of the total volume of space is filled with regions of density significantly lower than the average density. From these models we estimate that the average electron density in most of space is lower by at least a factor of 15 compared to the estimate based on one half of all baryons being uniformly distributed and ionized. Therefore the energy dependence of the photon-axion oscillations is consistent with experiment, and the oscillation model remains a viable alternative to the accelerating Universe for explaining the supernova observations. Furthermore, the electron density does give rise to a sufficiently large plasma frequency which cuts off the photon-axion mixing above microwave frequencies, shielding the cosmic microwave photons from axion conversions and significantly relaxing the lower bounds on the axion mass implied by the oscillation model.