Cosmological consequences of spontaneous lepton number violation in SO(10) grand unification

Abstract

Cosmological constraints on grand unified theories with spontaneous lepton number violation are analysed. We concentrate on SO(10), the simplest of the models possessing this property. It has been noted previously that the consistency of these models with the observed baryon asymmetry generically implies strict upper bounds on the light neutrino masses. In this paper, we analyze the situation in detail. We find that minimal models of fermion masses face difficulties, but that it is possible for these models to generate an adequate baryon asymmetry via non-equilibrium lepton number violating processes when the right-handed neutrino masses are near their maximum possible values. This condition uniquely picks out the minimal gauge symmetry breaking scheme. A non-minimal model is also analyzed, with somewhat different conclusions due to the nature of the imposed symmetries.

Leptogenesis

“…Early analyses, focusing on hierarchical singlet neutrinos, include [51][52][53][54] (see the thesis [55] for details, in particular an analysis of supersymmetric leptogenesis using superfield formalism). The importance of including the wave function renormalisation of the decaying singlet, in calculating the CP asymmetry, was recognised in [56].…”

Baryogenesis from the weak scale to the grand unification scale

“…where Early studies of leptogenesis were partly motivated by trying to find alternatives to electroweak baryogenesis, which did not seem to produce a big enough asymmetry. Several extensions of the Standard Model with hierarchical heavy neutrino masses were found which could explain the observed value of the baryon asymmetry (Gherghetta and Jungman, 1993;Langacker et al, 1986;Luty, 1992). At this time models with keV-scale light neutrinos were still considered.…”

Baryon asymmetry and dark matter

“…The natural theoretical framework for extensions of the standard model with righthanded neutrinos are unified theories based on the gauge group SO (10). Corresponding models of leptogenesis [3,4] can indeed explain the observed baryon asymmetry. Assuming a hierarchy of neutrino masses similar to the known mass hierarchy of up-type quarks, one obtains a rather large temperature for baryogenesis, T B ∼ 10 10 GeV [4], which can be reached in inflationary models after reheating [5].…”