On the Viability of Minimal Neutrinophilic Two-Higgs-Doublet Models

TL;DR

This paper evaluates the constraints of electroweak precision data on neutrinophilic two-Higgs-doublet models, finding that models with a $ ext{Z}_2$ symmetry are nearly ruled out, while others are tightly constrained but still viable.

Contribution

It provides the first detailed analysis of electroweak constraints on neutrinophilic two-Higgs-doublet models with specific symmetries, highlighting their viability and limitations.

Findings

The $ ext{Z}_2$ symmetric model is almost ruled out by data.

Models with a global $U(1)$ symmetry remain viable but are highly constrained.

Charged and neutral scalars must have nearly degenerate masses.

Abstract

We study the constraints that electroweak precision data can impose, after the discovery of the Higgs boson by the LHC, on neutrinophilic two-Higgs-doublet models which comprise one extra $SU(2)\times U(1)$ doublet and a new symmetry, namely a spontaneously broken $\mathbb{Z}_2$ or a softly broken global $U(1)$. In these models the extra Higgs doublet, via its very small vacuum expectation value, is the sole responsible for neutrino masses. We find that the model with a $\mathbb{Z}_2$ symmetry is basically ruled out by electroweak precision data, even if the model is slightly extended to include extra right-handed neutrinos, due to the presence of a very light scalar. While the other model is still perfectly viable, the parameter space is considerably constrained by current data, specially by the $T$ parameter. In particular, the new charged and neutral scalars must have very similar masses.