Dirac neutrinos in the 2HDM with restrictive Abelian symmetries

TL;DR

This paper explores how a two-Higgs-doublet extension of the Standard Model can naturally produce small Dirac neutrino masses through restrictive symmetry-based textures, aligning with experimental data and predicting specific phenomenological consequences.

Contribution

It identifies the most restrictive lepton mass matrix textures compatible with data that can be realized by Abelian symmetries in the 2HDM, establishing relations among Yukawa couplings and neutrino parameters.

Findings

Only 5 out of 28 textures are realizable by Abelian symmetries in the 2HDM.

One-to-one relations between Yukawa couplings and neutrino parameters are established.

Predictions for lepton universality and lepton-flavor-violating processes are discussed.

Abstract

Recently, there has been a growing interest in extensions of the Standard Model in which naturally small Dirac neutrino masses arise due to existence of a symmetry which protects neutrino's Diracness. Motivated by this, we consider an extension of the Standard Model with a second Higgs doublet (2HDM) and three right-handed neutrinos where lepton number is conserved and, thus, neutrinos are Dirac particles. In this framework, we identify the most restrictive texture-zero combinations for the Dirac-neutrino and charged-lepton mass matrices that lead to masses and mixings compatible with current experimental data. We then investigate, in a systematic way, which of these combinations can be realized by Abelian continuous U(1) or discrete $\mathbb{Z}_N$ symmetries. We conclude that, from the 28 initially possible sets of maximally-restricted lepton mass matrices, only 5 have a symmetry realization in the 2HDM. For these cases, one-to-one relations among the Yukawa couplings and the neutrino mass and mixing parameters are established, and the fermion interactions with the neutral and charged scalars of the 2HDM are also determined. Consequences for lepton universality in $\tau$ decays and rare lepton-flavor-violating processes are also discussed.