Non-universal soft scalar masses in supersymmetric theories

The existence of non--universal soft masses is the most general situation in supersymmetric theories. We study the consecuences that this situation has for the low--energy sparticle spectrum. In particular, we analize in detail the contribution to the scalar mass renormalization group equations of the $U(1)_Y$ D--term. We obtain analytic expressions for the evolution of masses of the three generations and these allow us to show that such a contribution can produce important modifications on the spectrum. The necessity to avoid flavour changing neutral currents does not constrain this result. Finally, we discuss a realistic example in the context of string theory where the departure from universality is large.