Weinberg dimension-5 operator by vector-like lepton doublets

TL;DR

This paper proposes a new way to generate the Weinberg dimension-5 operator for neutrino masses using vector-like lepton doublets, which can also produce baryon asymmetry and fit into grand unified theories.

Contribution

It introduces a novel mechanism involving vector-like lepton doublets for neutrino mass generation and baryogenesis, expanding beyond traditional seesaw models.

Findings

Vector-like lepton doublets can induce the Weinberg operator at tree level.

Heavy fermion singlets or triplets can generate lepton asymmetry for baryogenesis.

The scenario is compatible with grand unification theories.

Abstract

It is well known that a Weinberg dimension-5 operator for small neutrino masses can be realized at tree level in three types of renormalizable models: (i) the type-I seesaw mediated by fermion singlets, (ii) the type-II seesaw mediated by Higgs triplets, (iii) the type-III seesaw mediated by fermion triplets. We here point out such operator can be also induced at tree level by vector-like lepton doublets in association with unusual fermion singlets, Higgs triplets or fermion triplets. If these unusual fermion singlets, Higgs triplets or fermion triplets are heavy enough, their decays can generate a lepton asymmetry to explain the cosmic baryon asymmetry, meanwhile, the vector-like lepton doublets can lead to a novel inverse or linear seesaw with rich observable phenomena. We further specify our scenario can be naturally embedded into a grand unification theory without the conventional type-I, type-II or type-III seesaw.