Dark Matter signals at the LHC from a 3HDM

Abstract

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, H2→H1ff¯f=u,d,c,s,b,e,μ,τ $$ {H}_2\to {H}_1f\overline{f}\left(f=u,d,c,s,b,e,\mu, \tau \right) $$, 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→H1H2→H1H1ff¯ $$ h\to {H}_1{H}_2\to {H}_1{H}_1f\overline{f} $$ into two DM particles and di-leptons/di-jets, where h is produced from either gluon-gluon Fusion (ggF) or Vector Boson Fusion (VBF). However, this signal competes with the tree-level channel qq¯→H1H1Z∗→H1H1ff¯ $$ q\overline{q}\to {H}_1{H}_1{Z}^{\ast}\to {H}_1{H}_1f\overline{f} $$. We devise some benchmarks, compliant with collider, DM and cosmological data, for which the interplay between these modes is discussed. In particular, we show that the resulting detector signature, , with invariant mass of ff¯ $$ f\overline{f} $$ much smaller than m Z , can potentially be extracted already during Run 2 and 3. For example, the H 2 → H 1 γ * and γ * → e + e − case will give a spectacular QED mono-shower signal.

Keywords

• Beyond Standard Model
• Dark matter
• Hadron-Hadron scattering (experiments)
• Higgs physics