Lepton flavor violation ine±e−→l±e−(l=μ,τ)induced byR-conserving supersymmetry

Abstract

The lepton-flavor-violating signals ${e}^{+}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathcal{l}}^{+}{e}^{\ensuremath{-}}$ and ${e}^{\ensuremath{-}}{e}^{\ensuremath{-}}\ensuremath{\rightarrow}{\mathcal{l}}^{\ensuremath{-}}{e}^{\ensuremath{-}}(\mathcal{l}=\ensuremath{\mu},\ensuremath{\tau})$ are studied in the context of low-energy R-parity-conserving supersymmetry at center-of-mass energies of interest for the next generation of linear colliders. Loop level amplitudes receive contributions from electroweak penguin and box diagrams involving sleptons and gauginos. Lepton flavor violation is due to off-diagonal elements in a ${\mathrm{SU}(2)}_{L}$ doublet slepton mass matrix. These masses are treated as model-independent free phenomenological parameters in order to discover regions in parameter space where the signal cross section may be observable. The results are compared with (a) the experimental bounds from the nonobservation of rare radiative lepton decays $\ensuremath{\mu},\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\tau}}e\ensuremath{\gamma}$ and (b) the general MSUGRA theoretical scenario with the seesaw mechanism where off-diagonal slepton matrix entries are generated by renormalization group evolution of neutrino Yukawa couplings induced by the presence of new energy scales set by the heavy ${\mathrm{SU}(2)}_{L}$ singlet neutrino masses. It is found that in ${e}^{\ensuremath{-}}{e}^{\ensuremath{-}}$ collisions the $(e\ensuremath{\tau})$ signal can be observable with a total integrated luminosity of $100{\mathrm{fb}}^{\ensuremath{-}1}$ and the background can be easily suppressed. In ${e}^{+}{e}^{\ensuremath{-}}$ collisions the cross section is smaller and higher luminosities are needed. The experimental bound on the decay $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\mu}}e\ensuremath{\gamma}$ prevents the $(e\ensuremath{\mu})$ signal from being observable.