Electroweak Precision Measurements and the Minimal Supersymmetric Standard Model

Abstract

We discuss supersymmetric contributions to the electroweak precision measurements in the Minimal Supersymmetric Standard Model for two cases: the quark-lepton universality violation $δ_{q\ell}$ in charged currents and the ratio $R_b=Γ(Z\rightarrow b\bar{b})/Γ(Z\rightarrow \rm hadrons)$. The recent experimental data suggest deviations from the Standard Model for these observables, at the 1-$σ$ level for the former and at more than 3-$σ$ level for the latter. We analyze the non-oblique corrections from the SUSY particles to explain these discrepancies. The observed non-zero $δ_{q\ell}$ may be explained by relatively light sleptons, charginos and neutralinos. Although the observed excess of $R_b$ can be explained by very light scalar top and chargino for low $\tanβ$, this interpretation is severely constrained by the opening of exotic decay modes for the top quark.