Ultralight Dirac neutrinos from nearly degenerate Higgs doublets

TL;DR

This paper proposes a model with nearly degenerate Higgs doublets and mirror symmetry that naturally generates ultralight Dirac neutrinos through a suppressed Dirac seesaw mechanism, differing from traditional approaches.

Contribution

It introduces a novel Higgs doublet symmetry framework that explains tiny neutrino masses via vacuum expectation value differences and mirror symmetry, offering an alternative to conventional neutrino mass models.

Findings

Neutrino masses are proportional to the difference of Higgs VEVs.

Charged fermion masses are proportional to the sum of Higgs VEVs.

The model effectively mimics a high-suppression Dirac seesaw mechanism.

Abstract

Two Higgs doublets respect a mirror symmetry with spontaneous violation so that their vacuum expectation values can realize a small difference. Under this symmetry, three newly introduced right-handed neutrinos rather than the standard model fermions perform an odd transformation. Accordingly the neutrino masses and the charged fermion masses respectively are proportional to the difference and sum of the vacuum expectation values of two Higgs doublets. From a phenomenological perspective, such nearly degenerate Higgs doublets with large cancellation are equivalent to a Dirac seesaw mechanism with high suppression.