Flavor Seesaw Mechanism

TL;DR

The paper introduces a new fermion mass generation mechanism involving vector-like fermions and a seesaw process, explaining fermion mass hierarchies and predicting testable flavor-violation signals.

Contribution

It proposes a novel model with vector-like fermions and a seesaw mechanism that naturally explains fermion mass hierarchies and predicts observable flavor-violation effects.

Findings

Third and second generation masses arise at tree level via seesaw.

First generation masses generated by loop corrections.

Neutrinos naturally have only Dirac masses.

Abstract

In the Standard Model, Yukawa couplings parametrize the fermion masses and mixing angles with the exception of neutrino masses. The hierarchies and apparent regularities among the quark and lepton masses are, however, otherwise a mystery. We propose a new class of models having vector-like fermions that can potentially address this problem and provide a new mechanism for fermion mass generation. The masses of the third and second generations of quarks and leptons arise at tree level via the seesaw mechanism from new physics at moderately higher scales, while loop corrections produce the masses for the first generation. This mechanism has a number of interesting and testable consequences. Among them are unavoidable flavor-violating signals at the upcoming experiments and the fact that neutrinos have naturally only Dirac masses.