Testing lepton-flavor-violating decay of doubly charged Higgs bosons in type-II seesaw via photon fusion at the high-energy LHC

Tiny neutrino masses can be explained by the type-II seesaw mechanism, where a triplet scalar under $SU(2{)}_L$ is predicted. Collider searches for this exotic scalar have been extensively conducted, especially for its doubly charged component ${\mathrm{\Delta }}^{\pm \pm }$. Utilizing the forward detectors at the Large Hadron Collider (LHC), we study the probing sensitivity for the elastic photon fusion production of the scalars $pp\to p(\gamma \gamma \to {\mathrm{\Delta }}^{++}{\mathrm{\Delta }}^{--})p$ followed by the lepton-flavor-violating (LFV) decay channels ${\mathrm{\Delta }}^{\pm \pm }\to e^{\pm }{\mu }^{\pm }$. With a high center-of-mass energy of 100 TeV and several luminosity scenarios, we can extensively broaden the exclusion bounds in the parametric space of Br$({\mathrm{\Delta }}^{\pm \pm }\to e^{\pm }{\mu }^{\pm })$ versus the triplet scalar mass $m_{\mathrm{\Delta }}$. Specifically, at the 100 TeV LHC with an integrated luminosity of 3 ab${}^{-1}$, the mass exclusion limit at 95% C.L. can reach around 1150 GeV with the assumption of inverted neutrino mass hierarchy.