Neutrino emission in cold neutron stars: Bremsstrahlung and modified urca rates reexamined

TL;DR

This paper reevaluates neutrino emission rates in cold neutron stars, correcting previous models and providing improved formulas, which are crucial for understanding neutron star cooling and physics beyond the standard model.

Contribution

The authors correct and refine the standard neutrino emission rates in neutron stars, including the effects of rho meson exchange and removing simplifying assumptions, with comprehensive analytical formulas.

Findings

Cooling rates are reduced by up to a factor of 2.

Rho meson exchange effects are more significant than previously thought.

The new formulas facilitate accurate numerical modeling of neutron star cooling.

Abstract

Neutrino emission in cold neutron stars is dominated by the modified urca (murca) process and nucleon-nucleon bremsstrahlung. The standard emission rates were provided by Friman and Maxwell in 1979, effectively based on a chiral Lagrangian framework with pion and rho meson exchange, supplemented by Landau parameters to describe short-range interactions. We reevaluate these rates within the same framework, correcting several errors and removing unnecessary simplifications, notably the triangular approximation - where the Fermi momenta of protons and leptons negligible compared to that of neutrons - in MURCA, and quantify their importance. The impact of rho meson exchange, previously argued to cancel with interference effects, is actually quite relevant. Altogether, the cooling rates are reduced by as much as a factor 2. We provide comprehensive analytical formulas encompassing all contributions, designed for straightforward numerical implementation. Our results are particularly relevant for studies of physics beyond the standard model, where the emission of new particles - such as axions - is typically computed within the same framework we adopt here.