Multi-step phase transitions and gravitational waves in the inert doublet model

TL;DR

This paper investigates the complex phase transition history and gravitational wave signals in the inert doublet model, highlighting potential detectability by future gravitational wave observatories and collider experiments.

Contribution

It provides a comprehensive analysis of multi-step phase transitions and gravitational wave signals in the inert doublet model, incorporating latest collider and dark matter constraints.

Findings

Most phase transitions are single-step, but some involve multiple steps.

Gravitational wave signals from certain transitions could be detected by LISA, BBO, or DECIGO.

Direct detection experiments can probe multi-step transition parameter space.

Abstract

The inert doublet model is a well-motivated extension of the Standard Model that contains a dark matter candidate and modifies the dynamics of the electroweak symmetry breaking. In order to detail its phenomenology, we perform a comprehensive study of cosmic phase transitions and gravitational wave signals implied by the framework, accounting for the latest results of collider experiments. We require the neutral inert scalar to constitute, at least, a subdominant part of the observed dark matter abundance. While most of the phase transitions proceed through a single step, we identify regions of the parameter space where the electroweak vacuum is reached after multiple phase transitions. The resulting gravitational wave spectrum is generally dominated by single-step transitions and, in part of the parameter space, falls within the reach of future gravitational wave detectors such as LISA, BBO or DECIGO. We find that direct detection experiments efficiently probe the part of parameter space associated with multi-step phase transitions, which remain unconstrained only in the Higgs resonance region testable with future monojet searches. The implications of the new determination of the $W$ boson mass are also discussed.