Leptogenesis beyond the limit of hierarchical heavy neutrino masses

Abstract

We calculate the baryon asymmetry of the Universe in thermal leptogenesis beyond the usual lightest right-handed (RH) neutrino dominated scenario (N 1 DS) and in particular beyond the hierarchical limit (HL), M 1 ≪ M 2 ≪ M 3 , for the RH neutrino mass spectrum. After providing some orientation among the large variety of models, we first revisit the central role of the N 1 DS, with new insights on the dynamics of the asymmetry generation and then discuss the main routes departing from it, focusing on models beyond the HL. We study in detail two examples of 'strong-strong' washout scenarios: one with 'maximal phase' and the limit of very large M 3 , studying the effects arising when δ 2 ≡ (M 2 − M 1 )/M 1 is small. We extend analytical methods already applied to the N 1 DS showing, for example, that, in the degenerate limit (DL), the efficiency factors of the RH neutrinos become equal with the single decay parameter replaced by the sum. Both cases disprove the misconception that close RH neutrino masses necessarily lead to a final asymmetry enhancement and to a relaxation of the lower bounds on M 1 and on the initial temperature of the radiationdominated expansion. We also explain why leptogenesis tends to favor normal hierarchy compared to inverted hierarchy for the left-handed neutrino masses.

Consequences of minimal seesaw with complex μτ antisymmetry of neutrinos

“…Therefore, in general, only ε α 1 is the pertinent quantity in a hierarchical leptogenesis scenario. Nevertheless, there are certain circumstances in which the decays of N 2,3 do affect the final baryon asymmetry [87][88][89]. Furthermore, flavor plays an important role in the phenomenon of leptogenesis [83][84][85][86].…”

Leptogenesis in the two right-handed neutrino model revisited

“…In the case of an initial thermal abundance, the efficiency factors at the production are approximately given by [9,21,30] …”

“…In [8] a systematic leptogenesis study of this model was performed, also with texture zeros in the neutrino Dirac mass matrix, considering lepton flavour violating processes within supersymmetric scenarios. Leptogenesis with two RH neutrinos has been also studied beyond the hierarchical limit, obtaining the precise conditions both for the degenerate limit and for the hierarchical limit to be recovered [9].…”

Successful leptogenesis inSO(10)unification with a left–right symmetric seesaw mechanism

“…[29] is not sufficient to tell whether leptogenesis can indeed be successful. The purpose of the present paper is to perform a careful, quantitative study of leptogenesis in supersymmetric SO(10) models with a left-right symmetric seesaw mechanism, taking into account the lepton flavour dynamics [40]- [53], as well as the contribution of the next-to-lightest right-handed neutrino supermultiplet [22,23,52,54,55]. As is well known from studies performed in the type I case, flavour effects can significantly enhance the final baryon asymmetry if there is a hierarchy between the washout parameters for different lepton flavours [41,42,43], and their impact might be crucial for solutions (±, ± , −) and (±, −, +).…”