Phenomenology of the Inert (2+1) and (4+2) Higgs Doublet Models

TL;DR

This paper explores extended inert Higgs doublet models, analyzing their phenomenology, dark matter candidates, and distinctive Higgs decay signatures, including new decay channels and cascade processes, with implications for collider experiments.

Contribution

It introduces and studies the phenomenology of the I(2+1)HDM and I(4+2)HDM models, extending previous inert doublet models with additional scalar doublets and analyzing their unique signatures.

Findings

Neutral inert scalars provide viable dark matter candidates.

New Higgs decay channels into photons and missing energy are identified.

Cascade decays of heavy Higgs states offer distinctive collider signatures.

Abstract

We make a phenomenological study of a model with two inert doublets plus one Higgs doublet (I(2+1)HDM) which is symmetric under a Z$_2$ group, preserved after Electro-Weak Symmetry Breaking (EWSB) by the vacuum alignment $(0,0,v)$. This model may be regarded as an extension to the model with one inert doublet plus one Higgs doublet (I(1+1)HDM), by the addition of an extra inert scalar doublet. The neutral fields from the two inert doublets provide a viable Dark Matter (DM) candidate which is stabilised by the conserved $Z_2$ symmetry. We study the new Higgs decay channels offered by the scalar fields from the extra doublets and their effect on the Standard Model (SM) Higgs couplings, including a new decay channel into photon(s) plus missing energy, which distinguishes the I(2+1)HDM from the I(1+1)HDM. Motivated by Supersymmetry, which requires an even number of doublets, we then extend this model into a model with four inert doublets plus two Higgs doublets (I(4+2)HDM) and study the phenomenology of the model with the vacuum alignment $(0,0,0,0,v,v)$. This scenario offers a wealth of Higgs signals, the most distinctive ones being cascade decays of heavy Higgs states into inert ones. Finally, we also remark that the smoking-gun signature of all the considered models is represented by invisible Higgs decays into the lightest inert Higgs bosons responsible for DM.