Global Electroweak Fits and Gauge Coupling Unification

Abstract

The purpose of this paper is threefold: a) Check if the rather poor Standard Model (SM) fit to all electroweak data can be improved in its minimal supersymmetric extension (MSSM); b) Check what constraints present electroweak data has on the parameter space of the supergravity inspired Constrained MSSM (CMSSM); c) Check if with the present high precision of the gauge coupling constants exact gauge coupling unification is still possible. The value of tan\beta in the CMSSM is constrained to be above 6.5, while the value of the gaugino masses at the GUT scale has to be above 220 GeV, which corresponds to a lower limit on the lightest neutralino (chargino) of ca. 95 (175) GeV. It is shown that the larger values of \alpha_s from R_l and \sinw from A_FB are consistent with perfect gauge unification. The low \alpha_s value from the hadronic cross section is correlated with the fact that the number of neutrino flavours is 2\sigma below the known value of 3 in the SM, which is shown to correspond to a 3sigma deviation in the hadronic cross section. Lowering sigma_{had} by 3sigma brings alpha_s up to 0.12 and N_nu up to 3.