Minimal U(1) two-Higgs-doublet models for quark and lepton flavour

TL;DR

This paper systematically analyzes minimal Abelian symmetry-based two-Higgs-doublet models for quark and lepton flavor, identifying models compatible with experimental data and exploring their phenomenological implications.

Contribution

It introduces four minimal quark flavor models and three predictive lepton flavor models within the 2HDM framework, linking flavor patterns to experimental constraints.

Findings

Identified models with specific flavor patterns matching observed masses and mixings.

Predicted lower bounds on neutrino masses testable by future experiments.

Found scenarios with scalar masses below TeV scale accessible to current experiments.

Abstract

In the context of the 2HDM, and assuming that neutrinos acquire masses via the Weinberg operator, we perform a systematic analysis to determine the minimal quark and lepton flavour patterns, compatible with masses, mixing and CP violation data, realisable by Abelian symmetries. We determine four minimal models for quarks, where the number of independent parameters matches the number of observables. For the lepton sector, three minimal predictive models are identified. Namely, we find scenarios with a preference for the upper/lower octant of the $\theta_{23}$ atmospheric mixing angle, that exhibit lower bounds on the lightest neutrino masses currently probed by cosmology and testable at future neutrinoless double beta decay experiments, even for a normally-ordered neutrino masses. We investigate the phenomenology of each model taking into account all relevant theoretical, electroweak precision observables, scalar sector constraints, as well as stringent quark flavour processes such as $\overline{B} \rightarrow X_s \gamma$, $B_s \rightarrow \mu^- \mu^+$ and meson oscillations, and the charged lepton flavour-violating decays $e_\alpha^{-} \rightarrow e_\beta^{-} e_\gamma^{+} e_\delta^{-}$ and $e_\alpha \rightarrow e_\beta \gamma$. We show that, in some cases, Abelian flavour symmetries provide a natural framework to suppress flavour-changing neutral couplings and lead to scenarios featuring heavy neutral/charged scalar masses below the TeV scale within the reach of current experiments.