Constraints on R-parity violating couplings from lepton universality

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We analyze the one loop corrections to leptonic W and Z decays in an R-parity violating extension to the Minimal Supersymmetric Standard Model (MSSM). We find that lepton universality violation in the Z line-shape variables alone would strengthen the bounds on the magnitudes of the lambda' couplings, but a global fit on all data leaves the bounds virtually unchanged at |lambda'₃₃ₖ| < 0.42 and |lambda'₂₃ₖ| < 0.50 at the 2 sigma level. Bounds from W decays are less stringent: |lambda'₃₃ₖ| < 2.4 at 2 sigma, as a consequence of the weaker Fermilab experimental bounds on lepton universality violation in W decays. We also point out the potential of constraining R-parity violating couplings from the measurement of the Upsilon invisible width.