Analytic formulation of Leptogenesis with neutrino oscillation data employing the general parametrization for neutrino mass matrix

TL;DR

This paper derives an analytic expression for CP asymmetry in leptogenesis using a general neutrino mass matrix parametrization, evaluating minimal RHN masses needed to explain neutrino data and baryon asymmetry.

Contribution

It provides a new analytic formula for CP asymmetry in leptogenesis within a general neutrino mass framework, including hierarchical RHN spectra and different Higgs scenarios.

Findings

Analytic CP asymmetry expression derived for general parametrization.

Minimum RHN mass for successful leptogenesis can be as low as sphaleron decoupling temperature.

Both thermal and non-thermal leptogenesis scenarios analyzed.

Abstract

The observed neutrino oscillations and baryon asymmetry, unexplained by the Standard Model (SM), can both be accounted for by extending the SM to include Majorana right-handed neutrinos (RHNs). Tiny neutrino masses naturally arise through the Type-I seesaw mechanism, which involves lepton number violation. Meanwhile, the baryon asymmetry can be generated via leptogenesis, where the out-of-equilibrium decay of RHNs produces a lepton asymmetry that is partially converted into a baryon asymmetry through sphaleron processes. The Dirac Yukawa couplings play the crucial role for both Type-I seesaw and leptogenesis. In this work, we derive an analytic expression for the CP asymmetry parameter in a general parametrization. Focusing on a hierarchical RHN mass spectrum, we evaluate the lowest mass of the lightest RHN that reproduce both neutrino oscillation data and the observed baryon asymmetry. We study the case with two and three generations of RHNs for both thermal and non-thermal leptogenesis scenarios. Besides the standard Type-I seesaw involving SM Higgs doublet, we also examine the Type-I seesaw with a new neutrinophillic Higgs doublet. In this case for non-thermal leptogenesis, the minimum value for the lightest RHN mass can be as low as sphaleron decoupling temperature.