Limiting two-Higgs-doublet models

TL;DR

This paper updates constraints on two-Higgs-doublet models (2HDMs), focusing on explaining the muon g-2 anomaly, and finds that only type X models can satisfy all current theoretical and experimental bounds.

Contribution

It provides a comprehensive analysis of 2HDMs in light of muon g-2, combining various constraints and identifying viable models, especially type X, under current data.

Findings

Type X 2HDM can explain muon g-2 anomaly.

Electroweak constraints are evaded with specific scalar degeneracies.

Only type X models remain viable after all constraints.

Abstract

We update the constraints on two-Higgs-doublet models (2HDMs) focusing on the parameter space relevant to explain the present muon $g$$-$$2$ anomaly, $\Delta a_{\mu}$, in four different types of models, type I, II, "lepton specific" (or X) and "flipped" (or Y). We show that the strong constraints provided by the electroweak precision data on the mass of the pseudoscalar Higgs, whose contribution may account for $\Delta a_{\mu}$, are evaded in regions where the charged scalar is degenerate with the heavy neutral one and the mixing angles $\alpha$ and $\beta$ satisfy the Standard Model limit $\beta-\alpha \approx \pi /2$. We combine theoretical constraints from vacuum stability and perturbativity with direct and indirect bounds arising from collider and $B$~physics. Possible future constraints from the electron $g$$-$$2$ are also considered. If the 126 GeV resonance discovered at the LHC is interpreted as the light CP-even Higgs boson of the 2HDM, we find that only models of type X can satisfy all the considered theoretical and experimental constraints.