ARS Leptogenesis

TL;DR

This paper reviews the ARS leptogenesis scenario, focusing on quantum kinetic equations, parameter space, and the role of CP violation, providing a comprehensive analysis of conditions for successful leptogenesis at the electroweak scale.

Contribution

It offers a detailed comparison of theoretical approaches, explores the viable parameter space with Bayesian methods, and clarifies the contributions of different CP-violating effects in ARS leptogenesis.

Findings

Viable parameter space for two right-handed neutrinos identified.

Rephasing invariants help classify dominant contributions.

Regions where lepton-number violating effects are significant mapped.

Abstract

We review the current status of the leptogenesis scenario originally proposed by Akhmedov, Rubakov and Smirnov (ARS). It takes place in the parametric regime where the right-handed neutrinos are at the electroweak scale or below and the CP-violating effects are induced by the coherent superposition of different right-handed mass eigenstates. Two main theoretical approaches to derive quantum kinetic equations, the Hamiltonian time evolution as well as the Closed-Time-Path technique are presented, and we discuss their relations. For scenarios with two right-handed neutrinos, we chart the viable parameter space. Both, a Bayesian analysis, that determines the most likely configurations for viable leptogenesis given different variants of flat priors, and a determination of the maximally allowed mixing between the light, mostly left-handed, and heavy, mostly right-handed, neutrino states are discussed. Rephasing invariants are shown to be a useful tool to classify and to understand various distinct contributions to ARS leptogenesis that can dominate in different parametric regimes. While these analyses are carried out for the parametric regime where initial asymmetries are generated predominantly from lepton-number conserving, but flavor violating effects, we also review the contributions from lepton-number violating operators and identify the regions of parameter space where these are relevant.