2HDMs

The Two Higgs Doublet Model, often abbreviated as 2HDM, is a class of extensions to the Standard Model of particle physics. In the Standard Model, a single Higgs field is responsible for giving mass to fundamental particles through the Higgs mechanism. The 2HDM postulates the existence of two Higgs doublets instead of one.

These two doublets interact with the Standard Model fermions in different ways, leading to a richer spectrum of Higgs bosons. While the Standard Model has a single scalar Higgs boson, a 2HDM typically predicts the existence of five Higgs bosons: two CP-even scalars (one of which can be identified with the observed Standard Model Higgs boson), one CP-odd scalar, and a pair of charged scalars.

The specific properties of these additional Higgs bosons depend on the chosen model within the 2HDM framework. Different versions, such as Type I, Type II, Lepton-specific, and Vector-like 2HDMs, define how the two Higgs doublets couple to up-type quarks, down-type quarks, and charged leptons. These variations can lead to different predictions for the masses and interactions of the predicted Higgs bosons.

The motivation for studying 2HDMs arises from addressing certain theoretical issues within the Standard Model, such as the strong CP problem or providing a framework for electroweak symmetry breaking that might be more natural. Furthermore, these models can offer explanations for phenomena not covered by the Standard Model, potentially connecting to dark matter or baryogenesis. Experimental searches at particle colliders, such as the Large Hadron Collider (LHC), are actively looking for evidence of these additional Higgs bosons and other new physics predicted by 2HDMs. Discovering such particles would provide crucial insights into physics beyond the Standard Model.