Low-scale leptogenesis with three heavy neutrinos

Marco Drewes,Giorgio Arcadi,Asmaa Abada,Juraj Klaric,Michele Lucente,Valerie Domcke

doi:10.1007/jhep01(2019)164

Abstract

Leptogenesis induced by the oscillations of GeV-scale neutrinos provides a minimal and testable explanation of the baryon asymmetry of the Universe. In this work we extend previous studies invoking only two heavy neutrinos to the case of three heavy neutrinos. We find qualitatively new behaviour as a result of lepton number violating oscillations and decays, strong flavour effects in the washout and a resonant enhancement due to matter effects. An approximate global B-overline{L} symmetry (representing the difference of baryon and a generalised lepton number) can protect the light neutrino masses from large radiative corrections, while simultaneously providing the ingredients for the resonant enhancement of the lepton asymmetry due to thermal contributions to the heavy neutrino dispersion relations. This mechanism is particularly efficient for large heavy neutrino mixing angles near the current experimental limits, a regime in which leptogenesis is not feasible in the minimal scenario with two heavy neutrinos. In this new parameter regime, low-scale leptogenesis is testable by the LHC and other existing experiments.

Highlights

All elementary fermions with the exception of neutrinos are known to exist with both chiralities, left-handed and right-handed, in the Standard Model (SM) of particle physics
Projecting the high-dimensional data set consisting of all parameter points meeting the experimental constraints on to different physically meaningful two-dimensional planes, we illustrate the qualitative new features arising in the n = 3 case of “ freeze-in leptogenesis”
In the region of large mixings and for Mi below ∼ 20 GeV, displaced vertex searches at the LHC [9, 17, 18, 22, 23, 180, 181] could see thousands of events, assuming that displacements in the mm range can be resolved. This would allow for a determination of the heavy neutrino flavour mixing pattern [35, 36], which is crucial to test the hypothesis that these particles are responsible for leptogenesis [74, 79]

Summary

Introduction

All elementary fermions with the exception of neutrinos are known to exist with both chiralities, left-handed and right-handed, in the Standard Model (SM) of particle physics. [1] for an overview Most importantly, they can generate non-zero neutrino masses mi that explain the light neutrino flavour oscillations via the type-I seesaw mechanism [2,3,4,5,6,7]. A key prediction of the seesaw mechanism is the existence of heavy neutrino mass states Ni with masses Mi mi and weak interactions with the SM leptons a (with a = e, μ, τ ) which are suppressed by small mixing angles θai. A lepton collider could offer an ideal tool to search for heavy neutrinos with masses below the W mass [27,28,29,30,31,32,33,34,35,36]. Searches at smaller masses Mi < 5 GeV are preformed at the NA62 experiment [37,38,39] as well as at T2K [40], and in the future at SHiP [31, 41]

Objectives

Results

Conclusion