Variations on Minimal Gauge Mediated Supersymmetry Breaking
  We study various modifications to the minimal models of gauge mediated supersymmetry breaking. We argue that, under reasonable assumptions, the structure of the messenger sector is rather restricted. We investigate the effects of possible mixing between messenger and ordinary squark and slepton fields and, in particular, violation of universality. We show that acceptable values for the $\mu$ and $B$ parameters can naturally arise from discrete, possibly horizontal, symmetries. We claim that in models where the supersymmetry breaking parameters $A$ and $B$ vanish at tree level, $\tan\beta$ could be large without fine tuning. We explain how the supersymmetric CP problem is solved in such models. 
Michael Dine, Yosef Nir and Yuri Shirman