Bounds on axion-like particles from the diffuse supernova flux

TL;DR

This paper derives new bounds on axion-like particles (ALPs) by analyzing the diffuse gamma-ray flux from supernovae, significantly constraining their couplings to photons and nucleons across a wide mass range.

Contribution

It provides the strongest constraints to date on ALP-photon couplings by using diffuse supernova flux measurements, considering both photon-only and nucleon-coupled ALPs.

Findings

Bounds on ALP-photon coupling are as low as 6×10⁻¹³ GeV⁻¹ for very light ALPs.

Including nucleon couplings greatly strengthens the constraints, reaching 10⁻¹⁹ GeV⁻¹ for MeV-mass ALPs.

Constraints cover a broad ALP mass range, from sub-eV to tens of MeV.

Abstract

The cumulative emission of Axion-Like Particles (ALPs) from all past core-collapse supernovae (SNe) would lead to a diffuse flux with energies ${\mathcal O}(50)$ 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 $g_{a\gamma} \lesssim 5 \times 10^{-10}~{\rm GeV}^{-1}$ for $m_a \lesssim 10^{-11}~{\rm eV}$, 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 $g_{a\gamma} \lesssim 6 \times 10^{-13}~{\rm GeV}^{-1}$ for the same mass range. If ALPs are heavier than $\sim$ 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. $g_{a\gamma} \lesssim 5 \times 10^{-11}~{\rm GeV}^{-1}$ for $m_a \sim 5~{\rm keV}$. Allowing for a (maximal) coupling to nucleons, the limit improves to the level of $g_{a\gamma} \lesssim 10^{-19}~{\rm GeV}^{-1}$ for $m_a \sim 20~{\rm MeV}$, which represents the strongest constraint to date.