Right-handed neutrino production rate at T > 160 GeV

TL;DR

This paper develops an interpolated formula for the production rate of right-handed neutrinos in the early universe, covering all mass and temperature regimes above 160 GeV, with implications for leptogenesis models.

Contribution

It introduces a unified approach to estimate right-handed neutrino production rates across different regimes, incorporating all-order resummation effects and providing tabulated results for practical use.

Findings

Provides a comprehensive interpolation formula for production rates.

Includes tabulated results for use in leptogenesis simulations.

Identifies a narrow intermediate regime where phenomenological modeling is needed.

Abstract

The production rate of right-handed neutrinos from a Standard Model plasma at a temperature above a hundred GeV has previously been evaluated up to NLO in Standard Model couplings (g ~ 2/3) in relativistic (M ~ pi T) and non-relativistic regimes (M >> pi T), and up to LO in an ultrarelativistic regime (M < gT). The last result necessitates an all-orders resummation of the loop expansion, accounting for multiple soft scatterings of the nearly light-like particles participating in 1 <-> 2 reactions. In this paper we suggest how the regimes can be interpolated into a result applicable for any right-handed neutrino mass and at all temperatures above 160 GeV. The results can also be used for determining the lepton number washout rate in models containing right-handed neutrinos. Numerical results are given in a tabulated form permitting for their incorporation into leptogenesis codes. We note that due to effects from soft Higgs bosons there is a narrow intermediate regime around M ~ g^{1/2} T in which our interpolation is phenomenological and a more precise study would be welcome.