Revisiting the SN1987A gamma-ray limit on ultralight axion-like particles

TL;DR

This paper revises the supernova SN1987A gamma-ray bound on ultralight axion-like particles by incorporating advanced supernova models and magnetic field data, resulting in a more accurate and stringent limit on their photon coupling.

Contribution

It provides a revised, more precise upper limit on ALP-photon coupling by updating supernova and magnetic field models, including nucleon effects and nuclear mass reductions.

Findings

New upper limit: g_{aγ} < 5.3 x 10^{-12} GeV^{-1} for m_a < 4.4 x 10^{-10} eV

Enhanced modeling reduces uncertainty in the gamma-ray bound

Discussion on future improvements with Fermi-LAT data

Abstract

We revise the bound from the supernova SN1987A on the coupling of ultralight axion-like particles (ALPs) to photons. In a core-collapse supernova, ALPs would be emitted via the Primakoff process, and eventually convert into gamma rays in the magnetic field of the Milky Way. The lack of a gamma-ray signal in the GRS instrument of the SMM satellite in coincidence with the observation of the neutrinos emitted from SN1987A therefore provides a strong bound on their coupling to photons. Due to the large uncertainty associated with the current bound, we revise this argument, based on state-of-the-art physical inputs both for the supernova models and for the Milky-Way magnetic field. Furthermore, we provide major amendments, such as the consistent treatment of nucleon-degeneracy effects and of the reduction of the nuclear masses in the hot and dense nuclear medium of the supernova. With these improvements, we obtain a new upper limit on the photon-ALP coupling: g_{a\gamma} < 5.3 x 10^{-12} GeV^{-1}, for m_a < 4.4 x 10^{-10} eV, and we also give its dependence at larger ALP masses. Moreover, we discuss how much the Fermi-LAT satellite experiment could improve this bound, should a close-enough supernova explode in the near future.