Probing Doubly Charged Higgs Bosons with Three-Body Associated Production at Future $e^{+}{e}^{-}$ Colliders

Abstract

We study the discovery prospects for a doubly charged Higgs boson $H^{\pm \pm }$ in the 2-Higgs doublet model with type-II seesaw at future $e^{+}{e}^{-}$ colliders. Focusing on the three-body channels $e^{+}{e}^{-}\to H^{\pm \pm }{H}_1^{\mp }{H}_1^{\mp }$ and $e^{+}{e}^{-}\to H^{\pm \pm }{H}_1^{\mp }{W}^{\mp }$, we scan the model parameter space subject to theoretical consistency as well as current collider, flavor and electroWeak precision observables (EWPOs). We find that these $2\to 3$ production modes can exceed the conventional pair-production rate $e^{+}{e}^{-}\to H^{++}{H}^{--}$, followed by $H^{\pm \pm }\to H_1^{\pm }{H}_1^{\pm }$ and $H_1^{\pm }{W}^{\pm }$ decays, over wide regions, particularly above the $H^{\pm \pm }\to H_1^{\pm }{H}_1^{\pm }$ and $H^{\pm \pm }\to H_1^{\pm }{W}^{\pm }$ thresholds, reaching cross sections up to $\mathcal{O}(10^2)$~fb for $\sqrt{s}=500$--$1500$~GeV. A detector-level analysis of the $4\ell +E_T^{\text{miss}}$ signature, including dominant multiboson and top quark backgrounds, shows that discovery sensitivity is achievable for $\sqrt{s}=1000$-$1500$~GeV with integrated luminosities in the few ab${}^{-1}$ range, even in the presence of realistic systematic uncertainties.

Comments: 16 pages, 9 figures, 13 tables, references added