Effective Lagrangian approach to nuclearμ−−e−conversion and the role of vector mesons

Abstract

We study nuclear ${\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{-}{e}^{\ensuremath{-}}$ conversion in the general framework of an effective Lagrangian approach without referring to any specific realization of the physics beyond the standard model (SM) responsible for lepton flavor violation ($\mathrm{L\ensuremath{\llap{\not\;}}}{\text{ }}_{f}$). We examine the impact of a specific hadronization prescription on the analysis of new physics in nuclear ${\ensuremath{\mu}}^{\ensuremath{-}}\ensuremath{-}{e}^{\ensuremath{-}}$ conversion and stress the importance of vector meson exchange between lepton and nucleon currents. A new issue of this mechanism is the presence of the strange quark vector current contribution induced by the $\ensuremath{\phi}$ meson. This allows us to extract new limits on the $\mathrm{L\ensuremath{\llap{\not\;}}}{\text{ }}_{f}$ lepton-quark effective couplings from the existing experimental data.