Light lepton portal dark matter meets the LHC

TL;DR

This paper investigates the potential of the LHC to detect light lepton portal dark matter models with scalar mediators below 10 GeV, focusing on collider signatures and current constraints.

Contribution

It provides the first detailed collider analysis of light lepton portal dark matter with scalar mass splitting, highlighting discovery prospects at the HL-LHC.

Findings

Significant parameter space can be tested at HL-LHC.

Complementarity between slepton and mono-Z searches enhances detection.

Same-sign scalar production is a distinctive model prediction.

Abstract

We examine the sensitivity of the Large Hadron Collider (LHC) to light lepton portal dark matter with its mass below 10$\,$GeV. The model features an extra doublet scalar field and singlet Dirac dark matter, which have Yukawa interactions with left-handed leptons. To correctly produce the dark matter abundance via the thermal freeze-out, a large mass splitting among the extra scalars is required, thus providing a light neutral scalar below ${\cal O}(10)$GeV and heavy neutral and charged scalars at the electroweak scale. In this paper, we focus on the electroweak pair-production of the extra scalars with subsequent model-specific scalar decays and evaluate the current constraints with the LHC Run$\,$2 data and the discovery potential at the High Luminosity LHC (HL-LHC). It turns out that a large part of the theoretically allowed parameter space can be tested at the HL-LHC by taking into account complementarity between slepton searches and mono-$Z$ plus missing transverse energy search. We also discuss same-sign charged scalar production as a unique prediction of the model, and the implication of the collider searches in the thermal dark matter scenario.