Searching for lepton portal dark matter with colliders and gravitational waves

TL;DR

This paper explores a lepton portal dark matter model, examining collider signals and gravitational wave signatures, with a focus on scalar couplings, Higgs interactions, and phase transition effects.

Contribution

It introduces the impact of scalar portal coupling on collider phenomenology and gravitational wave signals in lepton portal dark matter models, highlighting new detection channels and complementary probes.

Findings

Scalar portal coupling enhances LHC sensitivity via Higgs-mediated processes.

Future lepton colliders can measure the lepton portal coupling through off-shell production.

First-order phase transition in the scalar potential can generate detectable gravitational waves.

Abstract

We study the lepton portal dark matter (DM) model in which the relic abundance is determined by the portal coupling among the Majorana fermion DM candidate $\chi$, the singlet charged scalar mediator $S^\pm$ and the Standard Model (SM) right-handed lepton. The direct and indirect searches are not sensitive to this model. This article studies the lepton portal coupling as well as the scalar portal coupling (between $S^\pm$ and SM Higgs boson), as the latter is generally allowed in the Lagrangian. The inclusion of scalar portal coupling not only significantly enhances the LHC reach via the $gg\to h^*\to S^+S^-$ process, but also provides a few novel signal channels, such as the exotic decays and coupling deviations of the Higgs boson, offering new opportunities to probe the model. In addition, we also study the Drell-Yan production of $S^+S^-$ at future lepton colliders, and find out that the scenario where one $S^\pm$ is off-shell can be used to measure the lepton portal coupling directly. In particular, we are interested in the possibility that the scalar potential triggers a first-order phase transition and hence provides the stochastic gravitational wave (GW) signals. In this case, the terrestrial collider experiments and space-based GW detectors serve as complementary approaches to probe the model.