Axion signatures from supernova explosions through the nucleon electric-dipole portal

TL;DR

This paper explores how axions coupled via the nucleon electric-dipole moment could produce detectable signals from supernovae, offering a new way to search for axions and their effects beyond dark matter.

Contribution

It refines supernova bounds on axion emissions via the nucleon EDM portal and proposes a novel detection method through gamma-ray signals in neutrino detectors.

Findings

Refined supernova axion emission bounds.

Potential gamma-ray signals detectable by Hyper-Kamiokande.

Implications for cosmological extra-radiation.

Abstract

We consider axions coupled to nucleons and photons only through the nucleon electric-dipole moment (EDM) portal. This coupling is a model-independent feature of QCD axions, which solve the strong CP problem, and might arise as well in more general axion-like particle setups. We revise the supernova (SN) axion emission induced by the nucleon EDM coupling and refine accordingly the SN 1987A bound. Furthermore, we calculate the axion flux from a future Galactic SN and show that it might produce a peculiar and potentially detectable gamma-ray signal in a large underground neutrino detector such as the proposed Hyper-Kamiokande. The possibility to detect such a signal offers a way to search for an oscillating nucleon EDM complementary to CASPERe, without relying on the assumption that axions are a sizeable component of the dark matter. Furthermore, if axions from SN produce an observable signal, they could also lead to an amount of cosmological extra-radiation observable in future cosmic surveys.