Implications of a Purely Right-Handed Bottom Quark Decay Coupling

We examine the implications of the hypothesis that the decays of the b-quark occur via pure right-handed couplings. We show that the existing lower limits on neutrinoless double beta decay imply that any gauge model realizing this idea must have either an $L_e-L_\mu$ or $L_e-L_\tau$ symmetry. We then show that constraints of cosmology together with observations from SN1987A imply that the right-handed neutrinos in this model must be heavier than about 100 MeV in general. In one special case with the $L_e-L_\mu$ symmetry, the $\nu_{\tau_R}$ is heavier than 2 GeV so that this particular version of the model is already ruled out.