Displaced vertex signatures of doubly charged scalars in the type-II seesaw and its left-right extensions

Understand

The type-II seesaw mechanism with an isospin-triplet scalar $\Delta_L$ provides one of the most compelling explanations for the observed smallness of neutrino masses.

• The triplet contains a doubly-charged component $H_L^{\pm\pm}$, which dominantly decays to either same-sign dileptons or to a pair of $W$ bosons, depending on the size of the triplet vacuum expectation value.
• However, there exists a range of Yukawa couplings $f_L$ of the triplet to the charged leptons, wherein a relatively light $H_L^{\pm\pm}$ tends to be long-lived, giving rise to distinct displaced-vertex signatures at the high-energy colliders.
• We find that the displaced vertex signals from the leptonic decays $H_L^{\pm\pm} \to \ell_\alpha^\pm \ell_\beta^\pm$ could probe a broad parameter space with $10^{-10} \lesssim |f_L| \lesssim 10^{-6}$ and 45.6 GeV $< M_{H_L^{\pm\pm}} \lesssim 200$ GeV at the high-luminosity LHC.