Higgs and Supersymmetric Particle Signals at the Infrared Fixed Point of the Top Quark Mass

We study the properties of the Higgs and Supersymmetric particle spectrum, associated with the infrared fixed point solution of the top quark mass in the Minimal Supersymmetric Standard Model. We concentrate on the possible detection of these particles, analysing the deviations from the Standard Model predictions for the leptonic and hadronic variables measured at LEP and for the b → sγ decay rate. We consider the low and moderate tanβ regime, imposing the constraints derived from a proper radiative SU(2)L×U(1)Y symmetry breaking and we study both, the cases of universal and non–universal soft supersymmetry breaking parameters at high energies. In the first case, for any given value of the top quark mass, the Higgs and supersymmetric particle spectrum is completely determined as a function of only two soft supersymmetry breaking parameters, implying very definite experimental signatures. In the case of non–universal mass parameters at MGUT , instead, the strong correlations between the sparticle masses are relaxed, allowing a richer structure for the precision data variables. We show, however, that the requirement that the low energy theory proceeds from a grand unified theory with a local symmetry group including SU(5) strongly constrains the set of possible indirect experimental signatures. As a general feature, whenever a significant deviation from the Standard Model value of the precision data parameters is predicted, a light sparticle, visible at LEP2, appears in the model. CERN-TH.7393/94 July 1994