Dirac leptogenesis via scatterings

TL;DR

This paper demonstrates that in Dirac leptogenesis, matter-antimatter asymmetry can be generated through scatterings of Standard Model particles and Dirac neutrinos without requiring heavy particle decays, allowing lower reheating temperatures.

Contribution

It introduces a novel mechanism for leptogenesis relying solely on scatterings, eliminating the need for heavy particle production in the early universe.

Findings

Scatterings suffice to generate asymmetry in Dirac leptogenesis.

Reheating temperature can be below heavy particle mass scale.

Potential observational signatures include extra neutrinos and proton decay.

Abstract

Leptogenesis typically requires the introduction of heavy particles whose out-of-equilibrium decays are essential for generating a matter-antimatter asymmetry, according to one of Sakharov's conditions. We show that in Dirac leptogenesis, scatterings between the light degrees of freedom - Standard Model particles plus Dirac neutrinos - suffice to generate the asymmetry. Sakharov's conditions are satisfied because the right-handed neutrino partners are out of equilibrium. Consequently, heavy degrees of freedom never needed to be produced in the early universe, allowing for a reheating temperature below their mass scale. We solve the Boltzmann equations and discuss the viable parameter space together with observational signatures such as an increased number of effective neutrinos in the early universe as well as proton decay for some realizations.