A detailed comparison of LEP data with the predictions of the minimal supersymmetric SU(5) GUT

Abstract

We confront the precise LEP determinations of sin 2 θ w and the strong coupling α 3( m z 0 with the predictions of the minimal supersymmetric SU(5) GUT. We incorporate O( α em α 3) effects in the extraction of sin 2 θ w from LEP data. We incorporate distinct thresholds for the supersymmetric partners of the different species of Standard Model particles, parameterized in terms of a scalar mass m 0 and a gaugino mass m 1 2 that are assumed to be universal at the GUT scale. We also allow for uncertainties in the top, higgs and higgsino masses. We use the full two-loop renormalization group equations including top, bottom and tau Yukawa couplings. We show that GUT threshold effects are small because proton stability prevents triplet Higgs particles from weighing much less than 10 16 GeV. Using 1−σ errors for the experimental inputs and plausible ranges for unknown supersymmetric model parameters, in particular an upper bound of 300 GeV on the higgs mixing parameter μ, we find that either 3.0×10 12 TeV>m 1 2 >21 TeV or m 1 2 <65 GeV , with the intermediate range allowed at the 2 − σ level. An upper bound of μ=500 GeV excludes m 1 2 from 80 GeV to 5 TeV at 1 − σ, and an upper bound of μ=1 TeV excludes m 1 2 from 110 GeV to 620 GeV at 1 − σ. It is not possible at present to fix the supersymmetry breaking scale with any precision.