Short-range nuclear effects on axion emissivities by nucleon-nucleon bremsstrahlung

TL;DR

This paper reevaluates axion emission rates from nucleon-nucleon bremsstrahlung by incorporating short-range nuclear effects, revealing significant contributions and uncertainties that impact axion parameter constraints.

Contribution

It provides analytical formulas including full momentum dependence of nuclear potentials and assesses the impact of short-range effects on axion emission rates.

Findings

Two-pion exchange significantly affects emission rates.

Inclusion of nuclear effects can alter rates by a factor of ~24.

Uncertainty factor of ~4.9 impacts axion parameter bounds.

Abstract

The rates of axion emission by nucleon-nucleon (NN) bremsstrahlung are reconsidered by taking into account the NN short range correlations. The analytical formulas for the neutron-neutron (nn), proton-proton (pp) and neutron-proton (np) processes with the inclusion of the full momentum dependence of an one- and two- pion exchange nuclear potentials, in the non-degenerate limit, are explicitly given. We find that the two-pion exchange (short range) effects can give a significant contribution to the emission rates, and are temperature dependent. Other short range nuclear effects like effective nucleon mass, polarization effects and use of correlated wave functions, are discused as well. The trend of all these nuclear effects is to diminish the corresponding axion emission rates. Further, we estimate that the values of the emission rates calculated with the inclusion of all these effects can differ from the corresponding ones derived with constant nuclear matrix elements by a factor of $\sim 24$. This leads to an uncertainty factor of $\sim 4.9$ when extracting bounds of the axion parameters