Constraining the Inert Doublet Model at the LHC

TL;DR

This work assesses whether LHC searches optimized for a 2HDMa dark-matter scenario can constrain the Inert Doublet Model (IDM), which shares the same final states but features different production topologies. Using a MG5_aMC@NLO–Pythia–FastJet–CheckMATE pipeline, the authors recast ATLAS Z+MET, VBF Higgs invisible decays, and soft-lepton searches, revealing that topology and DM constraints critically shape exclusions. They find that the Z+MET channel with sole on-shell $HA$ production largely leaves IDM viable, while including subleading channels and DM constraints excludes more region, and VBF provides robust, model-independent limits on $m_H$ and $\lambda_{345}$ in the off-shell regime; the soft-lepton search further constrains compressed spectra with $\Delta m = m_A - m_H$ of a few GeV. Collectively, the results highlight the need for IDM-specific search strategies at the LHC and show how DM relic-density and direct-detection bounds play pivotal roles in sculpting the viable IDM parameter space.

Abstract

In this work, we analyze experimental exclusion bounds that have been derived within a specific new physics realization, the two Higgs-doublet model with a pseudoscalar singlet (2HDMa), and their application to a different model, the Inert Doublet Model (IDM), that features the same final state. In this context, we discuss the sensitivity of the ATLAS search for the 2HDMa in final states with leptons and missing energy. We demonstrate that, with cuts optimized for a specific model topology, other new physics scenarios with larger rates might yet escape detection. We also give an update on constraints from vector boson fusion production of the Standard Model-like scalar and subsequent invisible decay from full Run 2 data on the parameter space of the IDM, with a special emphasis on the off-shell region, as well as a search that specifically concentrates on soft lepton final states.

Figures (18)

• Figure 1: Production channel for $Z(\ell^+\ell^-)+E^\text{miss}_T$ final state in the 2HDMa.
• Figure 2: Bounds from direct detection in the $\left ( m_H, \lambda_{345}\right )$ plane, including points forbidden by direct detection from the LUX-ZEPLIN experiment LZ:2024zvo(brown) as well as points allowed by all constraints (red).
• Figure 3: Leading (top) and sub-leading (bottom left) and (bottom right) production channels for $Z(\ell^+\ell^-$)+MET final state in the IDM.
• Figure 4: Left: Contribution from various production processes to the $Z(\ell^+\ell^-$)+MET final state. The purple points (bar) denote the Drell-Yan cross section, i.e. on-shell $HA$ production and subsequent decay, the green points (cross) refer to the cross section of the full process $pp\rightarrow \ell^+\ell^-HH$. In the cyan points (star), the process involving charged scalars was added to the target process $pp\rightarrow \ell^+\ell^-HH$. Right: a subset of the points shown in the plot on the left panel, that satisfy the DM constraints.
• Figure 5: The parameter space for the $Z$ + MET signal in the $\left ( m_H, m_A\right )$ plane. In particular, DM constraints lead to the gap between 63 and 75 $$ GeV for the dark matter mass (see text for details). The scale of $m_A$ stems from requiring mainly on-shell decays into the target signature.