# Dark Matter Signals at the LHC from a 3HDM

## TL;DR

This paper investigates unique dark matter signals at the LHC within a 3-Higgs Doublet Model, focusing on cascade decays involving inert scalars and their potential observability through Higgs decay channels.

## Contribution

It introduces a novel dark matter signal in the 3HDM framework involving loop-induced decays, not possible in simpler models, highlighting a distinctive experimental signature.

## Key findings

- Loop-induced decay $H_2 o H_1 ar{f}f$ identified as a key signature.
- Cascade decay $h o H_1 H_2 o H_1 H_1 ar{f}f$ can be observed at the LHC.
- Signal is prominent when $H_2$ and $H_1$ are nearly degenerate.

## Abstract

We analyse new signals of Dark Matter (DM) at the Large Hadron Collider (LHC) in a 3-Higgs Doublet Model (3HDM) where only one doublet acquires a Vacuum Expectation Value (VEV), preserving a parity $Z_2$. The other two doublets are inert and do not develop a VEV, leading to a dark scalar sector controlled by $Z_2$, with the lightest CP-even dark scalar $H_1$ being the DM candidate. This leads to the loop induced decay of the next-to-lightest scalar, $H_2\to H_1\bar{f}f$ ($f=u,d,c,s,b,e,\mu,\tau$), mediated by both dark CP-odd and charged scalars. This is a smoking-gun signal of the 3HDM since it is not allowed in the 2HDM with one inert doublet and is expected to be important when $H_2$ and $H_1$ are close in mass. In practice, this signature can be observed in the cascade decay of the SM-like Higgs boson, $h\to H_1H_2\to H_1H_1\bar{f}f$ into two DM particles and di-leptons/di-jets, where $h$ is produced from either gluon-gluon Fusion (ggF) or Vector Boson Fusion (VBF).