Direct Urca neutrino radiation from superfluid baryonic matter

Abstract

Dense matter in compact stars cools efficiently by neutrino emission via the direct Urca processes n -> p + e + nu and p + e -> n + nu. Below the pairing phase transition temperature Tc these processes are suppressed - at asymptotically low temperatures exponentially. We compute the emissivity of the Urca process at one loop for temperatures T < Tc, in the case where the baryons are paired in the 1S0 partial wave. The Urca process is suppressed linearly, rather than exponentially, within the temperature range 0.1 < T/Tc < 1. The charge-current Cooper pair-breaking process contributes up to 50% of the total Urca emissivity in this temperature range.