Charged Higgs Pair Production Associated with Neutral Gauge Bosons at Future Multi-TeV Muon Colliders

The first results for charged Higgs pair production associated with a neutral gauge boson at future multi-TeV muon colliders are presented within the framework of the Two-Higgs-Doublet Model. In this phenomenological study, the viable parameter spaces of the Type-X and Type-II models are examined under relevant theoretical and experimental constraints. The two-body decay channels of the charged Higgs boson are evaluated, and the dominant branching fractions are identified within the allowed regions. The production cross sections also include initial-state radiation corrections up to two-loop order in this work. The signal significances for the production processes are then examined by scanning over the viable parameter space of the models. With the high integrated luminosity planned for future multi-TeV muon colliders, the production signals can be observed with a statistical significance exceeding 5σ for several selected points within the allowed parameter space.