Search

Abstract We propose a new theory of dark matter based on axion physics and cosmological phase transitions. We show that theories in which a gauge coupling increases through a first-order phase transition naturally result in ‘axion relic pockets’: regions of relic false vacua stabilised by the pressure from a kinematically trapped, hot axion gas. Axion relic pockets provide a viable and highly economical theory of dark matter: the macroscopic properties of the pockets depend only on a single parameter (the phase transition temperature). We describe the formation, evolution and present-day properties of axion relic pockets, and outline how their phenomenology is distinct from existing dark matter paradigms. We briefly discuss how laboratory experiments and astronomical observations can be used to test the theory, and identify gamma-ray observations of magnetised, dark-matter-dense environments as particularly promising.

Abstract The elusive nature of Dark Matter (DM) remains a mystery far from being solved. A vast effort is dedicated to search for signatures of feeble DM interactions with Standard Model particles. In this work, we explore the signatures of axion DM boosted by interactions with Supernova neutrinos: Neutrino-Boosted Axion DM ( $$\nu $$ ν BADM). We focus on $$\nu $$ ν BADM converting into photons in the Galactic magnetic field, generating a peculiar gamma-ray flux. This signal falls in the poorly explored MeV energy range, that will be probed by next generation gamma-ray missions. Once more, astrophysical searches might act as a probe of fundamental physics, unveiling the nature and properties of DM.

Abstract The detection of very high-energy neutrinos by IceCube experiment supports the existence of a comparable gamma-ray counterpart from the same cosmic accelerators. Under the likely assumption that the sources of these particles are of extragalactic origin, the emitted photon flux would be significantly absorbed during its propagation over cosmic distances. However, in the presence of photon mixing with ultra-light axion-like-particles (ALPs), this expectation would be strongly modified. Notably, photon-ALP conversions in the host galaxy would produce an ALP flux which propagates unimpeded in the extragalactic space. Then, the back-conversion of ALPs in the Galactic magnetic field leads to a diffuse high-energy photon flux. In this context, the recent detection of the diffuse high-energy photon flux by the Large High Altitude Air Shower Observatory (LHAASO) allows us to exclude at the $$95\%$$ 95 % CL an ALP-photon coupling $$g_{a\gamma } > rsim 3.9$$ g a γ ≳ 3.9 – $$7.8 \times 10^{-11}~\mathrm {GeV^{-1}}$$ 7.8 × 10 - 11 GeV - 1 for $$m_{a}\lesssim 4\times 10^{-7}~\textrm{eV}$$ m a ≲ 4 × 10 - 7 eV , depending on the assumptions on the magnetic fields and on the original gamma-ray spectrum. This new bound is complementary with other ALP constraints from very-high-energy gamma-ray experiments and sensitivities of future experiments.

We update the globular cluster bound on massive (ma up to a few 100 keV) axion-like particles (ALP) interacting with photons. The production of such particles in the stellar core is dominated by the Primakoff γ+Ze→Ze+a and by the photon coalescence process γ+γ→a. The latter, which is predominant at high masses, was not included in previous estimations. Furthermore, we account for the possibility that axions decay inside the stellar core, a non-negligible effect at the masses and couplings we are considering here. Consequently, our result modifies considerably the previous constraint, especially for ma≳50keV. The combined constraints from Globular Cluster stars, SN 1987A, and beam-dump experiments leave a small triangularly shaped region open in the parameter space around ma∼0.5−1MeV and gaγ∼10−5GeV−1. This is informally known as the ALP “cosmological triangle” since it can be excluded only using standard cosmological arguments. As we shall mention, however, there are viable cosmological models that are compatible with axion-like particles with parameters in such region. We also discuss possibilities to explore the cosmological triangle experimentally in upcoming accelerator experiments.