The CP-conserving two-Higgs-doublet model: the approach to the decoupling limit

TL;DR

This work analyzes the decoupling limit of the most general CP-conserving two-Higgs-doublet model, showing that a light CP-even Higgs can exhibit Standard-Model–like couplings when the heavier Higgs states are at a high scale. It derives the leading corrections to Higgs couplings in the approach to decoupling, identifies basis-invariant parameters, and details how hVV, hff, and Higgs self-couplings align with SM predictions as m_A^2 ≫ v^2. The paper also discusses parameter regions where a SM-like Higgs exists without true decoupling, and applies the framework to the MSSM, illustrating radiative effects and potential delays in decoupling. The results inform how precision Higgs measurements at future colliders could reveal or constrain non-minimal Higgs sectors and their underlying parameters.

Abstract

A CP-even neutral Higgs boson with Standard-Model-like couplings may be the lightest scalar of a two-Higgs-doublet model. We study the decoupling limit of the most general CP-conserving two-Higgs-doublet model, where the mass of the lightest Higgs scalar is significantly smaller than the masses of the other Higgs bosons of the model. In this case, the properties of the lightest Higgs boson are nearly indistinguishable from those of the Standard Model Higgs boson. The first non-trivial corrections to Higgs couplings in the approach to the decoupling limit are also evaluated. The importance of detecting such deviations in precision Higgs measurements at future colliders is emphasized. We also clarify the case in which a neutral Higgs boson can possess Standard-Model-like couplings in a regime where the decoupling limit does not apply. The two-Higgs-doublet sector of the minimal supersymmetric model illustrates many of the above features.