Two-Component Dark Matter in the Type-I 2HDM

TL;DR

This paper explores a two-component dark matter model within the type-I two-Higgs-doublet framework, analyzing thermal production, experimental constraints, and parameter space viability, revealing tensions between collider bounds and dark matter requirements.

Contribution

It introduces a novel two-component dark matter scenario in the type-I 2HDM with detailed analysis of thermal processes and experimental constraints, highlighting the impact of collider bounds on dark matter phenomenology.

Findings

Viable parameter regions satisfy relic abundance and detection constraints.

Collider bounds significantly restrict scalar sector parameters.

Tension exists between collider limits and dark matter phenomenology in sub-TeV masses.

Abstract

We investigate a two-component dark matter scenario in the type-I two-Higgs-doublet model. The dark sector contains a real scalar $s$ and a Dirac fermion $\chi$, whose stability is ensured by a $Z_4$ symmetry together with kinematic conditions. The scalar interacts with the visible sector through Higgs-portal couplings, while the fermion interacts with the scalar via Yukawa interactions. In this framework, we analyze the thermal freeze-out production of both candidates, accounting for annihilation, conversion, and semi-annihilation processes. A comprehensive scan over the multidimensional parameter space is performed in terms of physical masses, mixing angles, and portal couplings, imposing theoretical requirements such as perturbativity and vacuum stability. We confront the model with current experimental constraints, including the observed relic abundance, invisible Higgs decays, direct detection limits on spin-independent scattering cross sections, and electroweak precision observables. We find that viable regions of parameter space can satisfy all dark matter constraints, but collider bounds strongly constrain the scalar sector, narrowing the allowed regions and creating tension with those favored by dark matter phenomenology, particularly in the sub-TeV mass regime.