Large lepton number violation at colliders: predictions from the minimal linear seesaw mechanism

Small neutrino masses can be sourced by a tiny vacuum expectation value of a leptophilic Higgs doublet, and mediated by Quasi-Dirac heavy neutrinos. In such simplest linear seesaw picture the neutrino mass mediators can be accessible to colliders. We describe novel charged Higgs and heavy neutrino production mechanisms that can be sizeable at $e^+ e^-$, $e^- \gamma$, $pp$, or muon colliders and discuss some of the associated signatures. The oscillation length of the heavy neutrino mediators is directly related to the light neutrino mass ordering. Moreover, lepton number violation can be large despite the smallness of neutrino masses, and may shed light on the Majorana nature of neutrinos and the significance of basic symmetries in weak interaction.