LHC Mono-$W/Z$ Signatures as a Probe for Dark Matter Explanations of Astrophysical Excesses

TL;DR

This paper explores how LHC mono-W/Z signatures can test dark matter models that explain astrophysical excesses, focusing on the inert two-Higgs doublet model and its collider signatures.

Contribution

It introduces a channel-separation strategy to disentangle scalar mass splittings at the LHC, testing dark matter explanations of astrophysical anomalies.

Findings

Most parameter space consistent with astrophysical anomalies is testable at the HL-LHC.

Leptonic channel excludes neutral mass splittings 80-260 GeV.

Hadronic channel constrains neutral splittings 30-150 GeV and charged splittings 70-230 GeV.

Abstract

The inert two-Higgs doublet model (IDM) is a compelling framework for weakly interacting massive particles (WIMPs) linked to electroweak symmetry breaking. It can account for both the Galactic Center gamma-ray excess (GCE) and the AMS-02 antiproton anomaly while also satisfying relic density and direct detection constraints for dark matter (DM) masses in the $55-75$ GeV range. Three specific DM annihilation channels can be identified: Higgs resonance, $SA$ co-annihilation, and $SS\to WW^{\ast}$ annihilation. Among these, the DM mass range of $70-75$ GeV with dominant $SS\to WW^{\ast}$ annihilation has received less attention in collider searches. To validate this parameter space, we combine LHC searches for mono-$W/Z$ signatures. In particular, we develop a channel-separation strategy to disentangle the contributions of charged mass splitting ($\Delta^{\pm}$) and neutral mass splitting ($\Delta^0$) in the inert scalar sector at the LHC. Our results indicate that most of the parameter space consistent with these astrophysical anomalies in the $SS\to WW^{\ast}$ annihilation regime will be testable at the High-Luminosity LHC. Specifically, from the leptonic channel we obtain a $2\sigma$ exclusion limit of $80 \lesssim \Delta^0 \lesssim 260$ GeV, while the hadronic channel yields $30 \lesssim \Delta^0 \lesssim 150$ GeV and $70 \lesssim \Delta^{\pm} \lesssim 230$ GeV for $m_S = 70$ GeV.