Light adjoint scalars and unification at the string scale

Abstract

Following the suggestion of Bachas, Fabre and Yanagida (BFY), we analyze the gauge coupling unification at the two-loop order, in a supersymmetric scenario where scalars belonging to the adjoint representations contribute to the evolution of the couplings from intermediate scales onward, and the unification scale is pushed towards the string scale. Thereafter, we compare the masses of these adjoint scalars to the scale at which the hidden sector gauge coupling reaches the non-perturbative limit at the two-loop order for various possible hidden sector gauge groups motivated by the the conjecture of BFY that the masses of these adjoint scalars are related to gaugino condensation. We also compute the predictions for the top and bottom quark masses in this scenario and compare them with those of MSSM. The predicted bottom mass improves in the BFY scenario for smaller values of $α_s$.