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 ${\delta }_{q\ell }$ in charged currents and the ratio $R_b=\Gamma (Z\to b\bar{b})/\Gamma (Z\to \mathrm{hadrons})$. The recent experimental data suggest deviations from the Standard Model for these observables, at the 1-$\sigma$ level for the former and at more than 3-$\sigma$ level for the latter. We analyze the non-oblique corrections from the SUSY particles to explain these discrepancies. The observed non-zero ${\delta }_{q\ell }$ 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 $\tan \beta$, this interpretation is severely constrained by the opening of exotic decay modes for the top quark.

Comments: 11 pages, LaTeX, uses ptptex.sty, with uuencoded eps figures, Talk given by Y. Yamada at Yukawa International Seminar (YKIS) '95 ``From the Standard Model to Grand Unified Theories'', Kyoto, Japan, August 21--25, 1995. To appear in the Proceedings