Radiative transfer in stars by feebly interacting bosons

TL;DR

This paper develops a first-principles framework for radiative transfer of feebly-interacting bosons in stars, deriving explicit formulas for their luminosity across different regimes, and improving upon previous models for stellar FIB emission.

Contribution

It introduces a simplified yet comprehensive method for calculating FIB radiative transfer in stars, including explicit volume-integral expressions and bridging free-streaming to trapping regimes.

Findings

Derived explicit volume-integral formulas for FIB luminosity.

Identified the quasi-thermal emission from a 'FIB sphere' in the trapping limit.

Provided improved models over previous literature for supernova and horizontal-branch star FIB emission.

Abstract

Starting from first principles, we study radiative transfer by new feebly-interacting bosons (FIBs) such as axions, axion-like particles (ALPs), dark photons, and others. Our key simplification is to include only boson emission or absorption (including decay), but not scattering between different modes of the radiation field. Based on a given distribution of temperature and FIB absorption rate in a star, we derive explicit volume-integral expressions for the boson luminosity, reaching from the free-streaming to the strong-trapping limit. The latter is seen explicitly to correspond to quasi-thermal emission from a "FIB sphere" according to the Stefan-Boltzmann law. Our results supersede expressions and approximations found in the recent literature on FIB emission from a supernova core and, for radiatively unstable FIBs, provide explicit expressions for the nonlocal ("ballistic") transfer of energy recently discussed in horizontal-branch stars.