Leptogenesis from first principles in the resonant regime

TL;DR

This paper develops a first-principles quantum field theoretical approach to resonant leptogenesis, revealing that quantum effects reduce the asymmetry compared to classical Boltzmann calculations, especially for nearly degenerate neutrinos.

Contribution

It introduces an analytical solution to the Kadanoff-Baym equations for resonant leptogenesis, improving understanding of quantum effects on lepton asymmetry.

Findings

Resonant enhancement is smaller in the quantum approach than in Boltzmann calculations.

Quantum coherent transitions significantly affect the generated asymmetry.

Analytical and numerical results show corrections are important for small mass splittings.

Abstract

The lepton asymmetry generated by the out-of-equilibrium decays of heavy Majorana neutrinos with a quasi-degenerate mass spectrum is resonantly enhanced. In this work, we study this scenario within a first-principle approach. The quantum field theoretical treatment is applicable for mass splittings of the order of the width of the Majorana neutrinos, for which the enhancement is maximally large. The non-equilibrium evolution of the mixing Majorana neutrino fields is described by a formal analytical solution of the Kadanoff-Baym equations, that is obtained by neglecting the back-reaction. Based on this solution, we derive approximate analytical expressions for the generated asymmetry and compare them to the Boltzmann result. We find that the resonant enhancement obtained from the Kadanoff-Baym approach is smaller compared to the Boltzmann approach, due to additional contributions that describe coherent transitions between the Majorana neutrino species. We also discuss corrections to the masses and widths of the degenerate pair of Majorana neutrinos that are relevant for very small mass splitting, and compare the approximate analytical result for the lepton asymmetry with numerical results.