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Register a new userObservable signatures of enhanced axion emission from proto-neutron stars
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We perform general relativistic one-dimensional supernova (SN) simulations to identify observable signatures of enhanced axion emission from the pion induced reaction $pi^- + p rightarrow n + a$ inside a newly born proto-neutron 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 seconds. 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 seconds. 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.
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We find that sub-GeV neutrino portal bosons that carry lepton number can condense inside a proto-neutron star (newly born neutron star). These bosons are produced copiously and form a Bose-Einstein condensate for a range of as yet unconstrained coupling strengths to neutrinos. The condensate is a lepton number superfluid with transport properties that differ dramatically from those encountered in ordinary dense baryonic matter. We discuss how this phase could alter the evolution of proto-neutron stars and comment on the implications for neutrino signals and nucleosynthesis.
We test the hypothesis that the observed first-peak (Sr, Y, Zr) and second-peak (Ba) s-process elemental abundances in low metallicity Milky Way stars ($text{[Fe/H]} lesssim -0.5$), and the abundances of the intervening elements Mo and Ru, can be explained by a pervasive r-process contribution that originates in neutrino-driven winds from highly-magnetic and rapidly rotating proto-neutron stars (proto-NSs). To this end, we construct chemical evolution models that incorporate recent calculations of proto-NS yields in addition to contributions from AGB stars, Type Ia supernovae, and two alternative sets of yields for massive star winds and core collapse supernovae. For non-rotating massive star yields from either set, models without proto-NS winds underpredict the observed s-process peak abundances by $0.3$-$1,text{dex}$ at low metallicity, and they severely underpredict Mo and Ru at all metallicities. Models that include the additional wind yields predicted for proto-NSs with spin periods $P sim 2$-$5,text{ms}$ fit the observed trends for all these elements well. Alternatively, models that omit proto-NS winds but adopt yields of rapidly rotating massive stars, with $v_{rm rot}$ between $150$ and $300,text{km},text{s}^{-1}$, can explain the observed abundance levels reasonably well for $text{[Fe/H]}<-2$. These models overpredict [Sr/Fe] and [Mo/Fe] at higher metallicities, but with a tuned dependence of $v_{rm rot}$ on stellar metallicity they might achieve an acceptable fit at all [Fe/H]. If many proto-NSs are born with strong magnetic fields and short spin periods, then their neutrino-driven winds provide a natural source for Sr, Y, Zr, Mo, Ru, and Ba in low metallicity stellar populations. Spherical winds from unmagnetized proto-NSs, on the other hand, overproduce the observed Sr, Y, and Zr abundances by a large factor.
Probing the QCD axion dark matter (DM) hypothesis is extremely challenging as the axion interacts very weakly with Standard Model particles. We propose a new avenue to test the QCD axion DM via transient radio signatures coming from encounters between neutron stars (NSs) and axion minihalos around primordial black holes (PBHs). We consider a general QCD axion scenario in which the PQ symmetry breaking occurs before (or during) inflation coexisting with a small fraction of DM in the form of PBHs. The PBHs will unavoidably acquire around them axion minihalos with the typical length scale of parsecs. The axion density in the minihalos may be much higher than the local DM density, and the presence of these compact objects in the Milky Way today provides a novel chance for testing the axion DM hypothesis. We study the evolution of the minihalo mass distribution in the Galaxy accounting for tidal forces and estimate the encounter rate between NSs and the dressed PBHs. We find that the encounters give rise to transient line-like emission of radio frequency photons produced by the resonant axion-photon conversion in the NS magnetosphere and the characteristic signal could be detectable with the sensitivity of current and prospective radio telescopes.
The QCD axion is expected to form dense structures known as axion miniclusters if the Peccei-Quinn symmetry is broken after inflation. Miniclusters that have survived until today would interact with the population of neutron stars (NSs) in the Milky Way to produce transient radio signals from axion-photon conversion in the NS magnetosphere. Here, we quantify the rate, duration, sky location, and brightness of these interactions for two different minicluster internal density profiles. For both density profiles, we find that these interactions: will occur frequently ($mathcal{O}(1-100),mathrm{day}^{-1}$); last between a day and a few months; are spatially clustered towards the Galactic center; and can reach observable fluxes. Searching for these transient signatures, which are within the reach of current generation telescopes, therefore offers a promising pathway to discovering QCD axion dark matter.
Axions may make a significant contribution to the dark matter of the universe. It has been suggested that these dark matter axions may condense into localized clumps, called axion stars. In this paper we argue that collisions of dilute axion stars with neutron stars, of the type known as magnetars, may be the origin of most of the observed fast radio bursts. This idea is a variation of an idea originally proposed by Iwazaki. However, instead of the surface effect of Iwazaki, we propose a perhaps stronger volume effect caused by the induced time dependent electric dipole moment of neutrons.
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