Yukawa unification as a window into the soft supersymmetry breaking Lagrangian

We study Yukawa unification, including the effects of a physical neutrino mass consistent with the SuperKamiokande observations, in a string or D-brane inspired SU(4) x SU(2)(L) x SU(2)(R) model which allows the most general non-universal scalar and gaugino masses, including the usual D-term contributions which arise in SO(10). We investigate how the tight constraints from rare decays such as b-->s gamma and tau-->mu gamma can provide information about the family dependent supersymmetry breaking soft Lagrangian, for example the trilinears associated with the second and third family. Many of our results also apply to SO(10) to which the model approximately reduces in a limiting case. In both models we find that Yukawa unification is perfectly viable providing the non-universal soft masses have particular patterns. In this sense Yukawa unification acts as a window into the soft supersymmetry breaking Lagrangian.