Alpha_s and Gauge Coupling Unification in Flipped SU(5) Models with   Gauge-Mediated Supersymmetry Breaking
  We examine gauge coupling unification and prediction for $\alpha_s (M_Z)$ in minimal flipped SU(5) with gauge-mediated supersymmetry breaking. We include threshold corrections at weak scale, messenger scale and unification scale, and explicitly show that in this model there can be either \emph{one-step} or \emph{two-step} gauge coupling unification, depending on unification-scale threshold corrections. The experimental value of $\alpha_s (M_Z)$ constrains heavy particle masses in one-step unification. In the case of two-step unification, we examine the prediction for $\alpha_s (M_Z)$ with two-loop, light, messenger and heavy threshold corrections, and find it to be compatible with the updated experimental data. 
K.T. Mahanthappa and Sechul Oh (University of Colorado)