Degenerate scalar scenario of two Higgs doublet model with a complex singlet scalar

TL;DR

This paper explores a two Higgs doublet model with a complex singlet scalar where the imaginary part serves as dark matter, demonstrating that a degenerate scalar scenario can enable a strong first-order electroweak phase transition compatible with experimental constraints.

Contribution

The study introduces the degenerate scalar scenario in the two Higgs doublet model with a complex singlet scalar, showing its implications for electroweak phase transition and collider phenomenology.

Findings

Degenerate scalars suppress DM-quark scattering.

Strong first-order EWPT is achievable without conflicting with DM constraints.

Scalar trilinear coupling shifts could be tested at colliders.

Abstract

We study the two Higgs doublet model with a complex singlet scalar whose imaginary part acts as dark matter (DM). The scattering of DM and quarks, mediated by three CP-even scalars in this model, is suppressed when masses of CP-even scalars are degenerate; that is called the ``degenerate scalar scenario''. Based on this scenario, we show that the strong first-order electroweak phase transition (EWPT) can be achieved without conflicting with constraints from the DM relic density and the direct detection experiments. We also discuss a shift of scalar trilinear coupling from the Standard Model prediction, which could be a test of this model in collider experiments.