# Improved axion emissivity from a supernova via nucleon-nucleon bremsstrahlung

## TL;DR

This paper refines the calculation of axion emission in supernovae by including various physical effects, showing a significant reduction in predicted emissivity, which impacts axion mass bounds and future experimental searches.

## Contribution

It provides a comprehensive, self-consistent analysis of axion emissivity in supernovae, incorporating effects like pion mass, two-pion exchange, in-medium nucleon masses, and nucleon degeneracy, improving upon previous models.

## Key findings

- Axion emissivity is reduced by over an order of magnitude compared to basic models.
- The corrected OPE potential aligns with the on-shell T-matrix results.
- Implications for axion mass bounds and experimental searches are discussed.

## Abstract

The most efficient axion production mechanism in a supernova (SN) core is the nucleon-nucleon bremsstrahlung. This process has been often modeled at the level of the vacuum one-pion exchange (OPE) approximation. Starting from this naive recipe, we revise the calculation including systematically different effects, namely a non-vanishing mass for the exchanged pion, the contribution from the two-pions exchange, effective in-medium nucleon masses and multiple nucleon scatterings. Moreover, we allow for an arbitrary degree of nucleon degeneracy. A self consistent treatment of the axion emission rate including all these effects is currently missing. The aim of this work is to provide such an analysis. Furthermore, we demonstrate that the OPE potential with all the previous corrections gives rise to similar results as the on-shell T-matrix, and is therefore well justified for our and similar studies. We find that the axion emissivity is reduced by over an order of magnitude with respect to the basic OPE calculation, after all these effects are accounted for. The implications for the axion mass bound and the impact for the next generation experimental axion searches is also discussed.