2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/43939The $e^- e^-$ mode with lepton number $L=+2$ of the initial state is particularly suitable for studying lepton and flavor number violating reactions (LFV). In this brief report we give a summary of the study of two loop-level reactions which violate lepton and flavor numbers: we first consider seesaw type models with heavy Majorana neutrinos at the TeV scale and study the reactions $e^{-}e^{-} \to \ell^{-}\ell^{-}$, and then similar reactions $e^{-}e^{-} \to \ell^{-}e^{-}$ ($\ell=μ,τ$) in supersymmetric models where LFV is due to slepton mixing.5 pages, talk presented by M. Cannoni at LCWS04, International Conference on Linear Collider, 19-23 Aprile 2004, Paris, France, to appear in the proceedingsHigh Energy Physics - Phenomenologytext