In-medium enhancement of the modified Urca neutrino reaction rates

TL;DR

This paper demonstrates that modified Urca neutrino emission rates in neutron star cores are significantly enhanced near the direct Urca threshold due to in-medium effects, impacting neutron star cooling models.

Contribution

It introduces a new calculation of neutrino emission rates considering in-medium nucleon spectra and provides an approximate formula for use in neutron star cooling simulations.

Findings

Enhanced neutrino emission rates near the direct Urca threshold.

In-medium nucleon spectra significantly affect Urca process rates.

Provides a practical emissivity formula for neutron star cooling models.

Abstract

We calculate modified Urca neutrino emission rates in the dense nuclear matter in neutron star cores. We find that these rates are strongly enhanced in the beta-stable matter in regions of the core close to the direct Urca process threshold. This enhancement can be tracked to the use of the in-medium nucleon spectrum in the virtual nucleon propagator. We describe the in-medium nucleon scattering in the non-relativistic Bruckner-Hartree-Fock framework taking into account two-body as well as the effective three-body forces, although the proposed enhancement does not rely on a particular way of the nucleon interaction treatment. Finally we suggest a simple approximate expression for the emissivity of the n-branch of the modified Urca process that can be used in the neutron stars cooling simulations with any nucleon equation of state of dense matter.