Baryon asymmetry of the universe and new neutrino states

TL;DR

This paper examines how additional GeV-scale neutrino states could impact the baryon asymmetry of the universe, deriving constraints on their properties to prevent washout of the asymmetry.

Contribution

It provides new bounds on the mass splittings and nature of extra neutrino states to preserve baryon asymmetry in the early universe.

Findings

Extra neutrino states must be pseudo-Dirac with tiny mass splittings.

Lepton number violating interactions can wash out baryon asymmetry.

Constraints depend on the scale and flavor of baryogenesis.

Abstract

The presence of additional neutrino states with masses in the GeV range is allowed by electro-weak precision observables. However, these additional states can lead to lepton number violating interactions which potentially can wash out considerably any GUT scale generated or elsewise pre-existing baryon asymmetry. We discuss the resulting bounds on neutrino parameters and find that - unless the baryon asymmetry is created at or below the electroweak scale or in some flavor which is decoupled from interactions to the new neutrino states - these have to be pseudo-Dirac with mass splittings between the right-handed and left-handed states of less than about ten keV.