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Supersymmetry, Supergravity and Rb revisited in the light of LEP 2

J. Ellis, J. Lopez, D. Nanopoulos

hep-pharXiv:hep-ph/9612376

Abstract

A previous study of supersymmetric models has indicated that they are unlikely to make a large contribution to Rb. We revisit this analysis, taking into account the improved lower limits on sparticle masses provided recently by LEP 2 and the Tevatron, finding that a generic supersymmetric model cannot contribute more than about one-and-a-half current experimental standard deviations to Rb. We then specialize this analysis to minimal supergravity models with universal high-energy boundary conditions, and find a much more stringent upper bound Rsusyb < 0.0003. We discuss in detail why such models can only attain values of Rsusyb that are considerably smaller even than those obtainable in more general supersymmetric models.

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