Leptogenesis, neutrino masses and gauge unification

Abstract

Leptogenesis is considered in its natural context where Majorana neutrinos fit in a gauge unification scheme and therefore couple to some extra gauge bosons. The masses of some of these gauge bosons are expected to be similar to those of the heavy Majorana particles, and this can have important consequences for leptogenesis. In fact, the effect can go both ways. Stricter bounds are obtained on one hand due to the dilution of the CP-violating effect by new decay and scattering channels, while, in a re-heating scheme, the presence of gauge couplings facilitates the re-population of the Majorana states. The latter effect allows in particular for smaller Dirac couplings. * ncosme@ulb.ac.be 1 that is more precisely, the quantitym 1 = λ ν λ † ν 11 v 2 /M 1 for λ ν the left-handed neutrino Yukawa couplings matrix and M 1 the lightest Majorana mass.

A non supersymmetric SO(10) grand unified model for all the physics below M GUT

“…It turns out that the case M ν 1 > M W R is untenable, since the decays of Majorana neutrinos into two-body final states of the type N → l R + W R are too fast, thus causing X ∼ O(10 4 − 10 5 ) [70][71][72]. We then have to rely in a scenario where M ν 1 < M W R ; in this case, N 1 mainly decays into three-body final states, with a width given by:…”

Leptogenesis: beyond the minimal type I seesaw scenario

“…Since m W R = g R v R /2 ∼ v R , and since the SU (2) R coupling g R is a priori of order one (or equal to the SU (2) L coupling in the left-right symmetric case), this is the case only if m N 1,2,3 ∼ v R . In this case the main effect of the W R and Z R is a washout effect [145,146]. This effect is especially dangerous for the efficiency because W R gauge interactions induce scattering processes involving only one external right-handed neutrino: N e R →ū R d R , Nū R →ē R d R , N d R → e R u R .…”

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

“…As shown in Ref. [65], however, this effect can be practically neglected if M i /v R < 10 −2 , which turns out to be the case for i = 1, 2 in each of the 8 solutions (at least as long as N 1,2 are light enough to be thermally produced after reheating, i.e. M 1,2 10 11 GeV).…”