Leptophilic fermion WIMP: Role of future lepton colliders

The leptophilic weakly interacting massive particle (WIMP) is realized in a minimal renormalizable model scenario where scalar mediators with lepton number establish the WIMP interaction with the standard model leptons. We perform a comprehensive analysis for such a WIMP scenario for two distinct cases with an SU(2) doublet or singlet mediator, considering all of the relevant current theoretical, cosmological, and experimental constraints. We show that monophoton searches at near-future lepton collider experiments (ILC, FCC-ee, CEPC, etc.) can play a significant role in probing the yet unexplored parameter range allowed by the WIMP relic density constraint. This will complement the search prospects at the near-future hadron collider experiment HL-LHC. Furthermore, we discuss the combined model scenario including both the doublet and singlet mediators. The combined model is capable of explaining the long-standing muon g − 2 anomaly, which is an additional advantage. We demonstrate that the region allowed by the latest muon ( g − 2 ) result, which has been updated very recently at Fermi National Accelerator Laboratory, can also be probed at future colliders and thus will be a simultaneous authentication of the model scenario.