Abstract
We will investigate the scenario in which the Standard Model (SM) Higgs sector and its two-doublet extension (called the Two Higgs Doublet Model or 2HDM) are the “portal” for the interactions between the Standard Model and a fermionic Dark Matter (DM) candidate. The latter is the lightest stable neutral particle of a family of vector-like leptons (VLLs). We will provide an extensive overview of this scenario combining the constraints coming purely from DM phenomenology with more general constraints like Electroweak Precision Test (EWPT) as well as with collider searches. In the case that the new fermionic sector interacts with the SM Higgs sector, constraints from DM phenomenology force the new states to lie above the TeV scale. This requirement is relaxed in the case of 2HDM. Nevertheless, strong constraints coming from EWPTs and the Renormalization Group Equations (RGEs) limit the impact of VLFs on collider phenomenology.
Highlights
C (2017) 77:456 are instead very popular, rather constrained [16,17,18,19,20], since a Dark Matter (DM) spin-0 (1), even if it is a singlet with respect to the Standard Model (SM) gauge group, can interact with the SM Higgs doublet H via four-field operators connecting the bilinear H H † with a DM pair and giving rise, after electroweak (EW) symmetry breaking, to an effective vertex between a DM pair and the physical Higgs field h
We have performed an extensive study of the impact of the addition of a family of vector-like fermions, with suitable quantum numbers such as to provide a DM candidate, to the SM and to various types of 2HDMs
Lower DM masses can instead be achieved in 2HDM realizations
Summary
We will review how introducing vector-like leptons affects the SM Higgs sector. First of all, they generate additional loop contributions to the couplings of the Higgs boson to two photons, giving rise to deviations of the corresponding signal strength with respect to the SM prediction. The presence of vector-like leptons is typically associated with sensitive departures from experimental limits for the EW precision observables. In order to have viable values of the Higgs signal strengths and precision observables, one should impose definite relations for the Yukawa couplings and masses of the new VLLs. The same relations will hold, up to slight modifications, in the 2HDM case
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