Can $\gamma\gamma$ collisions rival $e^-e^+$ in probing doubly charged Higgs bosons?

Abstract

High-energy $\gamma\gamma$ collisions, realizable as an operational mode of future lepton linear colliders such as the ILC and CLIC, provide a promising environment to probe extended Higgs sectors. We investigate the sensitivity of such colliders to doubly charged Higgs bosons within the 2-Higgs Doublet Model with type-II seesaw (2HDMcT). Focusing on the three-body production channels $\gamma\gamma \to H^{\pm\pm}H_1^{\mp}H_1^{\mp}$ and $\gamma\gamma \to H^{\pm\pm}H_1^{\mp}W^{\mp}$, we perform a parameter space scan consistent with theoretical constraints as well as current collider, flavor, and electroweak precision observables (EWPOs). We show that $\gamma\gamma$ collisions can rival the discovery potential of the conventional $e^+e^-$ mode for probing doubly charged Higgs bosons through a $4\ell+E_T^{miss}$ signature ($\ell=e,\mu$). Despite the reduced effective luminosity resulting from the photon spectrum, the significantly enhanced production cross sections, exceeding those in electron-positron collisions by more than one order of magnitude, compensate for this limitation. By performing a detailed signal-to-background analysis at center-of-mass energies of $\sqrt{s}=830$ and $1245$ GeV, we demonstrate that a discovery significance at the $5\sigma$ level can be achieved for viable benchmark points (BPs).