Constraints on R-parity violating couplings from lepton universality

We analyze the one loop corrections to leptonic W and Z decays in an R-parity violating extension to the minimal supersymmetric standard model. We find that lepton universality violation in the Z line-shape variables alone would strengthen the bounds on the magnitudes of the λ^′ couplings, but a global fit on all data leaves the bounds virtually unchanged at |λ_33k^′|<~0.42 and |λ_23k^′|<~0.50 at the 2σ level. Bounds from W decays are less stringent: |λ_33k^′|<~2.4 at 2σ, 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 Υ invisible width.