Search

We investigate the potential of type II supernovae (SNe) to constrain axionlike particles (ALPs) coupled simultaneously to nucleons and electrons. ALPs coupled to nucleons can be efficiently produced in the SN core via nucleon-nucleon bremsstrahlung and, for a wide range of parameters, leave the SN unhindered, producing a large ALP flux. For masses exceeding 1 MeV, these ALPs would decay into electron-positron pairs, generating a positron flux. In the case of Galactic SNe, the annihilation of the created positrons with the electrons present in the Galaxy would contribute to the 511 keV annihilation line. Using the spectrometer on integral observation of this line allows us to exclude a wide range of the axion-electron coupling, 10-19≲gae≲10-11, for gap∼10-9. Additionally, ALPs from extra-galactic SNe decaying into electron-positron pairs would yield a contribution to the cosmic x-ray background. In this case, we constrain the ALP-electron coupling down to gae∼10-20. [ABSTRACT FROM AUTHOR]

The Milky Way magnetic field can trigger conversions between photons and axionlike particles (ALPs), leading to peculiar features on the observable photon spectra. Previous studies considered only the regular component of the magnetic field. However, observations consistently show the existence of an additional turbulent component, with a similar strength and correlated on a scale of a few 10 pc. We investigate the impact of the turbulent magnetic field on the ALP-photon conversions, characterizing the effects numerically and analytically. We show that the turbulent magnetic field can change the conversion probability by up to a factor of two and may lead to observable irregularities in the observable photon spectra from different astrophysical sources. [ABSTRACT FROM AUTHOR]

We present a mechanism wherein the QCD axion coupling to nucleons, photons, or electrons can be enhanced selectively without increasing the axion mass. We focus in particular on the axion-nucleon couplings that are generally considered to be largely model independent, and we show how nucleophilic axion models can be constructed. We discuss the implications of a nucleophilic axion for astrophysics, cosmology, and laboratory searches. We present a model with enhanced axion couplings to nucleons and photons that can provide an excellent fit to the anomalous emission of hard x-rays recently observed from a group of nearby neutron stars, and we argue that such a scenario can be thoroughly tested in forthcoming axion-search experiments. [ABSTRACT FROM AUTHOR]

The cumulative emission of axionlike particles (ALPs) from all past core-collapse supernovae (SNe) would lead to a diffuse flux with energies O(50) MeV. We use this to constrain ALPs featuring couplings to photons and to nucleons. ALPs coupled only to photons are produced in the SN core via the Primakoff process and then converted into gamma rays in the Galactic magnetic field. We set a bound on gaγ≲5×10-10 GeV-1 for ma≲10-11 eV, using recent measurements of the diffuse gamma-ray flux observed by the Fermi-LAT telescope. However, if ALPs couple also with nucleons, their production rate in SN can be considerably enhanced due to the ALPs nucleon-nucleon bremsstrahlung process. Assuming the largest ALP-nucleon coupling phenomenologically allowed, bounds on the diffuse gamma-ray flux lead to a much stronger gaγ≲6×10-13 GeV-1 for the same mass range. If ALPs are heavier than ~keV, the decay into photons becomes significant, leading again to a diffuse gamma-ray flux. In the case of only photon coupling, we find, e.g., gaγ≲5×10-11 GeV-1 for ma~5 keV. Allowing for a (maximal) coupling to nucleons, the limit improves to the level of gaγ≲10-19 GeV-1 for ma~20 MeV, which represents the strongest constraint to date. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We perform general relativistic one-dimensional supernova (SN) simulations to identify observable signatures of enhanced axion emission from the pion-induced reaction π-+p→n+a inside a newly born protoneutron star (PNS). We focus on the early evolution after the onset of the supernova explosion to predict the temporal and spectral features of the neutrino and axion emission during the first 10 s. Pions are included as explicit new degrees of freedom in hot and dense matter. Their thermal population and their role in axion production are both determined consistently to include effects due to their interactions with nucleons. For a wide range of ambient conditions encountered inside a PNS, we find that the pion-induced axion production dominates over nucleon-nucleon bremsstrahlung processes. By consistently including the role of pions on the dense matter equation of state and on the energy loss, our simulations predict robust discernible features of neutrino and axion emission from a galactic supernova that can be observed in terrestrial detectors. For axion couplings that are compatible with current bounds, we find a significant suppression with time of the neutrino luminosity during the first 10 s. This suggests that current bounds derived from the neutrino signal from SN 1987A can be improved and that future galactic supernovae may provide significantly more stringent constraints. [ABSTRACT FROM AUTHOR]

The Sun is a well-studied astrophysical source of axionlike particles (ALPs), produced mainly through the Primakoff process. Moreover, in the Sun there exist large-scale magnetic fields that catalyze an additional ALP production via a coherent conversion of thermal photons. We study this contribution to the solar ALP emissivity, typically neglected in previous investigations. Furthermore, we discuss additional bounds on the ALP-photon coupling from energy-loss arguments, and the detection perspectives of this new ALP flux at future helioscope and dark matter experiments. [ABSTRACT FROM AUTHOR]