Small Dirac neutrino masses andRparity from anomalousU(1)symmetry

We suggest that many of the free parameters in the supersymmetric extensions of the standard model can be all linked together to the existence of a nonuniversal $U\left(1\right)\mathrm{}$ gauge symmetry, which has been spontaneously broken at very high scale. Such a symmetry can easily generate, via nonrenormalizable operators, appropriate tree level fermion mass textures as well as the $\mu$ term of the Higgs potential. We give a general parametrization of those terms. As output, R parity breaking terms only appear at a nonrenormalizable level and are linked to the Yukawa couplings, giving rise to the possibility of having effective (exact) R parity conservation. As an interesting application of this idea we explore the case where the neutrinos are Dirac particles. The scenario can be embedded in an extended SU(5) unification theory where the extra right handed neutrinos are introduced as singlets. Such a theory has exact R parity conservation and a sneutrino as the lightest supersymmetric particle.