Probing a degenerate-scalar scenario in a pseudoscalar dark-matter model

TL;DR

This paper investigates a pseudoscalar dark-matter model with degenerate scalars, showing how this degeneracy suppresses detection signals and proposing collider methods to verify the scenario.

Contribution

It introduces a degenerate-scalar scenario in a pseudoscalar dark-matter model and analyzes its experimental signatures and detectability at future colliders.

Findings

Dark-matter--nucleon scattering is suppressed in the degenerate-scalar scenario.

The model can satisfy current direct detection and relic density constraints.

A pair of nearly degenerate states can be distinguished at the ILC with high significance.

Abstract

We study a pseudoscalar dark-matter model arising from a complex singlet extension of the standard model (SM), and show that the dark-matter--nucleon scattering is suppressed when two CP-even scalars are degenerate. In such a degenerate-scalar scenario we explore the model parameter space which satisfies constraints from the direct detection experiments and the relic density of dark matter. In addition, we discuss a possibility to verify such a scenario by using the recoil mass technique at the International Linear Collider. We find that a pair of states separated by 0.2 GeV can be distinguished from the single SM-like Higgs state at 5$\sigma$ with integrated luminosity of 2 ab$^{-1}$.