Scalar sector of Two-Higgs-Doublet models: A mini-review

TL;DR

This mini-review examines the scalar sector of Two-Higgs-Doublet models (2HDM), focusing on parameter constraints from recent experimental data and theoretical considerations, including symmetries and stability.

Contribution

It provides a concise overview of 2HDM parametrizations, explores the impact of symmetries, and discusses current constraints on the model's parameter space in light of LHC findings.

Findings

Constraints from unitarity and stability limit 2HDM parameters.

Electroweak T-parameter imposes additional restrictions.

Symmetry choices (U(1) vs Z2) affect model properties.

Abstract

A vast literature on the theory and phenomenology of Two-Higgs-Doublet models (2HDM) exists since long. However, the present situation demands a revisit of some 2HDM properties. Now that a 125 GeV scalar resonance has been discovered at the LHC, with its couplings to other particles showing increasing affinity to the Standard Model Higgs-like behavior, the 2HDM parameter space is more squeezed than ever. We briefly review the different parametrizations of the 2HDM potential and discuss the constraints on the parameter space arising from the unitarity and stability of the potential together with constraints from the oblique electroweak $T$-parameter. We also differentiate the consequences of imposing a global continuous U(1) symmetry on the potential from a discrete $Z_2$ symmetry.