Leptogenesis from Heavy Right-Handed Neutrinos in CPT Violating Backgrounds

TL;DR

This paper investigates leptogenesis driven by heavy right-handed neutrinos in a CPT-violating background, using analytical solutions with Pade approximants to Boltzmann equations, revealing increased lepton asymmetry compared to previous estimates.

Contribution

It introduces a novel method employing Pade approximants to solve Boltzmann equations in leptogenesis models with CPT violation, including thermal momentum modes for the first time.

Findings

Lepton asymmetry is doubled when thermal momentum modes are included.

The new analysis aligns with previous estimates within 12.5% uncertainty.

The method may be applicable to broader cosmological problems.

Abstract

We discuss leptogenesis in a model with heavy right-handed Majorana neutrinos propagating in a constant but otherwise generic CPT-violating axial time-like background (which could be motivated by string theory considerations). At temperatures much higher than the temperature of the electroweak phase transition we solve analytically but approximately (using Pade approximants) the corresponding Boltzmann equations, which describe lepton asymmetry generation due to the tree-level decays of the heavy neutrinos into standard model leptons. These leptons are effectively massless at such temperatures. The current work completes in a rigorous way a preliminary treatment of the same system, by some of the present authors. In this earlier work, lepton asymmetry was crudely estimated considering the decay of a right-handed neutrino at rest. Our present analysis includes thermal momentum modes for the heavy neutrino and this leads to a total lepton asymmetry which is bigger by a factor of two as compared to the previous estimate. Nevertheless, our current and preliminary results for the freezeout are found to be in agreement (within a 12.5% uncertainty). Our analysis depends on a novel use of Pade approximants to solve the Boltzmann equations and may be more widely useful in cosmology.