A smoking gun signature of the 3HDM

Abstract

We analyse new signals of a 3-Higgs Doublet Model (3HDM) at the Large Hadron Collider (LHC) where only one doublet acquires a Vacuum Expectation Value (VEV), preserving a Z2 parity. The other two doublets are \textit{inert} and do not develop a VEV, leading to a \textit{dark scalar sector} controlled by Z2, with the lightest CP-even dark scalar H1 being the Dark Matter (DM) candidate. This leads to the loop induced decay of the next-to-lightest scalar, H2→H1ℓℓ¯ (ℓ=e,μ), mediated by both dark CP-odd neutral and charged scalars. This is a smoking-gun signal of the 3HDM since it is not allowed in the 2-Higgs Doublet Model (2HDM) with one inert doublet and is expected to be important when H2 and H1 are close in mass. In practice, this signature can be observed in the cascade decay of the SM-like Higgs boson, h→H1H2→H1H1ℓℓ¯ into two DM particles and di-leptons or h→H2H2→H1H1ℓℓ¯ℓℓ¯ into two DM particles and four-leptons, where h is produced from gluon-gluon Fusion. In order to test the feasibility of these channels at the LHC, we devise some benchmarks, compliant with collider, DM and cosmological data, for which the interplay between these production and decay modes is discussed. In particular, we show that the resulting detector signatures, $\Et \ell \bar \ell$ or $\Et \ell \bar \ell \ell \bar \ell$, with the invariant mass of ℓℓ¯ pairs much smaller than mZ, can potentially be extracted already from Run 3 data and at the High-Luminosity phase of the LHC.

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ORCID for S. Moretti: orcid.org/0000-0002-8601-7246

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