Lepton parity in supersymmetric flavor models

We investigate supersymmetric models where neither R parity nor lepton numb er nor baryon number is imposed. The full high energy theory has an exact h orizontal U(1) symmetry that is spontaneously broken. Quarks and Higgs fiel ds carry integer horizontal charges but leptons carry half integer charges. Consequently, the effective low energy theory has two special features: a U(1) symmetry that is explicitly broken by a small parameter, leading to se lection rules, and an exact residual Z(2) symmetry, that is lepton parity. As concerns neutrino parameters, the Z(2) symmetry forbids contributions fr om R-p-violating couplings and the U(1) symmetry induces the required hiera rchy. As concerns baryon number violation, the Z(2) symmetry forbids proton decay and the U(1) symmetry provides sufficient suppression of double nucl eon decay and of neutron antineutron oscillations.