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 (MSSM). 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 2 σ level. Bounds from W decays are less stringent: |λ′_33k| ≤ 2.4 at 2 σ, 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.