# Lepton collider signatures of dark CP violation

## TL;DR

This paper explores a 3-Higgs Doublet Model with inert scalars allowing dark CP violation, predicting distinctive collider signatures involving inert Higgs pairs at electron-positron colliders.

## Contribution

It introduces a novel inert 3HDM with dark CP violation and identifies specific collider signatures as potential evidence.

## Key findings

- Inert Higgs pair production thresholds serve as signatures of dark CP violation.
- The model provides a dark matter candidate stabilized by a Z2 symmetry.
- Distinctive collider signatures can be observed at future e+e- colliders.

## Abstract

We study an extension of the Standard Model (SM) in which two copies of the SM Higgs doublet are added to the scalar sector. These extra doublets do not develop a vacuum expectation value, hence, they are \textit{inert}. This essentially leads to a 3-Higgs Doublet Model (3HDM) with 2 inert and 1 active scalar doublets, which we denote as I(2+1)HDM. We allow for CP-violation in the \textit{inert} sector, where the lightest \textit{inert} state is protected from decaying to SM particles through the conservation of a $Z_2$ symmetry, so that it is a Dark Matter (DM) candidate. For this scenario, we identify a smoking gun signature of dark CP-violation in the form of production thresholds of pairs of \textit{inert} neutral Higgs bosons at an $e^+e^-$ collider.