Light Gluinos and Unification of Couplings

Abstract

We analyze the implications of the light gluino scenario for the unification of gauge and Yukawa couplings within the minimal supersymmetric standard model. Within this scheme all fermionic supersymmetric particles are naturally light, while the scalar partners of quarks and leptons, together with the heavy Higgs doublet may be heavy. This implies both a bound on $\tan\beta < 2.3$, in order to fulfill the experimental constraints on the chargino masses, and a strong correlation between $\sin^2\theta_W(M_Z)$ and $\alpha_3(M_Z)$, due to the suppression of the supersymmetric threshold corrections to the low energy values of the gauge couplings. Assuming the scalar sparticles to be lighter than 10 TeV, the physical top quark mass is constrained to be 145 GeV $< M_T <$ 210 GeV for $\tan\beta>1$, while the strong gauge coupling values, $0.122\leq\alpha_3(M_Z) \leq 0.133$, are in good agreement with the measured LEP ones. We also show that a relaxation of some of the conventional assumptions is necessary in order to achieve radiative breaking of the electroweak symmetry within the grand unification scheme.