Fermion number violating effects in low scale leptogenesis

Shintaro Eijima,Mikhail Shaposhnikov

doi:10.1016/j.physletb.2017.05.068

Shintaro Eijima, Mikhail Shaposhnikov

Open Access

https://doi.org/10.1016/j.physletb.2017.05.068

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Abstract

The existence of baryon asymmetry and dark matter in the Universe may be related to CP-violating reactions of three heavy neutral leptons (HNLs) with masses well below the Fermi scale. The dynamical description of the lepton asymmetry generation, which is the key ingredient of baryogenesis and of dark matter production, is quite complicated due to the presence of many different relaxation time scales and the necessity to include quantum-mechanical coherent effects in HNL oscillations. We derive kinetic equations accounting for fermion number violating effects missed so far and identify one of the domains of HNL masses that can potentially lead to large lepton asymmetry generation boosting the sterile neutrino dark matter production.

Highlights

Though the canonical Standard Model (SM) has been completed by the discovery of the Higgs boson and may be a valid effective quantum field theory all the way up to the Planck scale it is inconsistent with a number of observations
This has led to the conclusion that the equilibrium period between Tin and Tout erases all the lepton asymmetry which could have been generated at freeze-in temperature Tin, requiring that the large lepton asymmetry needed for effective dark matter production must be created at T < Tout
The aim of the present paper is to show that the part of the lepton asymmetry generated at Tin can survive until the temperatures of sterile neutrino Dark Matter (DM) production ∼ 100 MeV, in-spite of the fact that heavy neutral leptons (HNLs) are well in thermal equilibrium between Tin and Tout

Summary

Introduction

Though the canonical Standard Model (SM) has been completed by the discovery of the Higgs boson and may be a valid effective quantum field theory all the way up to the Planck scale (for recent discussions see [1,2,3]) it is inconsistent with a number of observations. The estimates of the equilibration rates of N2,3 in [11, 15, 16] and in more recent works [31, 32] based on careful thermal field theory computations showed that for all parameter choices consistent with observed pattern of neutrino masses and oscillations the HNLs N2,3 enter in thermal equilibrium at some temperature Tin exceeding tens of GeV and go out of thermal equilibrium at temperatures Tout < Tin which can be as small as 1 GeV This has led to the conclusion that the equilibrium period between Tin and Tout erases all the lepton asymmetry which could have been generated at freeze-in temperature Tin , requiring that the large lepton asymmetry needed for effective dark matter production must be created at T < Tout.

Kinetic equations and helicity

Conclusions