Bounds on supersymmetry from electroweak precision analysis

Abstract

The Standard Model global fit to precision data is excellent. The Minimal Supersymmetric Standard Model can also fit the data well, though not as well as the Standard Model. At best, supersymmetric contributions either decouple or only slightly decrease the total χ 2, at the expense of decreasing the number of degrees of freedom. In general, regions of parameter space with large supersymmetric corrections from light superpartners are associated with poor fits to the data. We contrast results of a simple (oblique) approximation with full one-loop results, and show that for the most important observables the non-oblique corrections can be larger than the oblique corrections, and must be taken into account. We elucidate the regions of parameter space in both gravity- and gauge-mediated models which are excluded. Significant regions of parameter space are excluded, especially with positive supersymmetric mass parameter μ. We give a complete listing of the bounds on all the superpartner and Higgs boson masses. For either sign of μ, and for all supersymmetric models considered, we set a lower limit on the mass of the lightest CP-even Higgs scalar, m h ⩾ 78 GeV. Also, the first and second generation squark masses are constrained to be above 280 (325) GeV in the supergravity (gauge-mediated) model.