Flavour always matters in scalar triplet leptogenesis

TL;DR

This paper develops a flavour-covariant formalism for scalar triplet leptogenesis, demonstrating that flavour effects are crucial across all temperature regimes and significantly influence the predicted baryon asymmetry.

Contribution

It introduces a novel flavour-covariant approach to scalar triplet leptogenesis, highlighting the importance of flavour effects even when charged lepton Yukawa interactions are out of equilibrium.

Findings

Flavour effects cannot be neglected in scalar triplet leptogenesis.

Single flavour approximation can significantly misestimate baryon asymmetry.

Allowed parameter space for successful leptogenesis is substantially enlarged.

Abstract

We present a flavour-covariant formalism for scalar triplet leptogenesis, which takes into account the effects of the different lepton flavours in a consistent way. Our main finding is that flavour effects can never be neglected in scalar triplet leptogenesis, even in the temperature regime where all charged lepton Yukawa interactions are out of equilibrium. This is at variance with the standard leptogenesis scenario with heavy Majorana neutrinos. In particular, the so-called single flavour approximation leads to predictions for the baryon asymmetry of the universe that can differ by a large amount from the flavour-covariant computation in all temperature regimes. We investigate numerically the impact of flavour effects and spectator processes on the generated baryon asymmetry, and find that the region of triplet parameter space allowed by successsful leptogenesis is significantly enlarged.