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.

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

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