Constraints on leptogenesis from a symmetry viewpoint

TL;DR

This paper demonstrates that certain symmetry constraints in type I seesaw models prevent leptogenesis at leading order, especially in models with flavor symmetries leading to mass-independent mixing, due to the diagonal nature of relevant Yukawa couplings.

Contribution

It provides a symmetry-based proof that specific flavor models with mass-independent mixing cannot generate leptogenesis CP asymmetry at leading order.

Findings

Leptogenesis is forbidden in models with residual symmetries of the mass matrices.

Relevant Yukawa couplings are diagonal in the physical basis for these models.

Flavor models with mass-independent mixing do not produce leptogenesis CP asymmetry.

Abstract

It is shown that type I seesaw models based on the standard model Lagrangian extended with three heavy Majorana right-handed fields do not have leptogenesis in leading order, if the symmetries of mass matrices are also the residual symmetry of the Lagrangian. In particular, flavor models that lead to a mass-independent leptonic mixing have a vanishing leptogenesis CP asymmetry. Based on symmetry arguments, we prove that in these models the Dirac-neutrino Yukawa coupling combinations relevant for leptogenesis are diagonal in the physical basis where the charged leptons and heavy Majorana neutrinos are diagonal.