The $Z_3$ soft breaking in the I(2+1)HDM and its probes at present and future colliders

TL;DR

This paper investigates a Z3 symmetric three-Higgs-doublet model with two inert doublets and one active doublet, exploring its dark matter implications and potential collider signatures at the LHC and future electron-positron colliders.

Contribution

It introduces the concept of Hermaphrodite Dark Matter within the I(2+1)HDM and analyzes how Z3 soft breaking affects dark matter stability and collider phenomenology.

Findings

Two-component dark matter scenario with distinct CP properties.

Differential spectra can reveal the presence of two different dark matter components.

Potential detection channels at LHC and future colliders for the model.

Abstract

A $ Z_3 $ symmetric 3-Higgs Doublet Model (3HDM) with two inert doublets and one active doublet (that plays the role of the Higgs doublet), the so-called I(2+1)HDM, is studied. We discuss the behaviour of this 3HDM realisation when one allows for a $ Z_3 $ soft breaking term. Such a symmetry enables the presence of a two-component Dark Matter (DM) scenario in the form of "Hermaphrodite DM", where the two inert candidates have opposite CP parity and are protected by this discrete symmetry from decaying into Standard Model (SM) particles. Furthermore, the two DM states are potentially distinguishable from each other as they cannot be subsumed into a complex field, having different masses and gauge couplings. With this in mind, we study differential spectra with a distinctive shape from which the existence of two different DM component distributions could be easily inferred. We prove this to be possible at the Large Hadron Collider (LHC) via the $q\bar{q} \to 2l+H_1H_1$ and $q\bar{q} \to 2l+A_1A_1$ processes as well as at a future electron-positron machine via the $e^{+}e^{-} \to 2l+H_1H_1$ and $e^{+}e^{-} \to 2l+A_1A_1$ channels, where $l=e,\mu$.