Implications of supersymmetric models with naturalR-parity conservation

In the minimal supersymmetric standard model, the conservation of $R$ parity is phenomenologically desirable, but is ad hoc in the sense that it is not required for the internal consistency of the theory. However, if $B-L$ is gauged at very high energies, $R$ parity will be conserved automatically and exactly, provided only that all order parameters carry even integer values of $3(B-L)\mathrm{}$. We propose a minimal extension of the supersymmetric standard model in which $R$-parity conservation arises naturally in this way. This approach predicts the existence of a very weakly coupled, neutral chiral supermultiplet of particles with electroweak-scale masses and lifetimes which may be cosmologically interesting. Neutrino masses arise via an intermediate-scale seesaw mechanism, and a solution to the $\mu$ problem is naturally incorporated. The apparent unification of gauge couplings at high energies is shown to be preserved in this approach. We also discuss a next-to-minimal extension, which predicts a pair of electroweak-scale chiral supermultiplets with electric charge 2.