Unstable Heavy Majorana Neutrinos and Leptogenesis

TL;DR

This paper introduces a novel mechanism for generating lepton asymmetry through the decay of unstable heavy Majorana neutrinos, emphasizing the role of interference effects when neutrinos are produced out of equilibrium.

Contribution

It presents a new leptogenesis mechanism involving superpositions of heavy Majorana neutrinos with small mass differences, leading to a lepton asymmetry proportional to  m/ .

Findings

Lepton asymmetry is proportional to  m/  in the proposed mechanism.

Interference effects in neutrino decay rates are crucial for asymmetry generation.

The mechanism is relevant in out-of-equilibrium scenarios like preheating.

Abstract

We propose a new mechanism producing a non-vanishing lepton number asymmetry, based on decays of heavy Majorana neutrinos. If they are produced out of equilibrium, as occurs in preheating scenario, and are superpositions of mass eigenstates rapidly decaying, their decay rates contains interference terms provided the mass differences $\Delta m$ are small compared to widths $\Gamma$. The resulting lepton asymmetry, which is the analogue of the time-integrated CP asymmetry in $B^0-\bar{B}^0$ system, is found to be proportional to $\Delta m/\Gamma$.