Constraints on Majoron Models, Neutrino Masses and Baryogenesis

We derive strong contraints on the Yukawa couplings and the vacuum expectation value in the singlet majoron model, taking into account the possibility of a small gravitationally induced mass for the majoron. If the present baryon asymmetry was created earlier than at the electroweak phase transition, then to preserve it from the combined effects of lepton number violating interactions and electroweak sphalerons, we find that stringent constraints on the Yukawa couplings, $h < 10^{-7}$, and the majoron scale, $v_s < v_{EW}$, must be satisfied. We also carefully rederive baryogenesis bounds on neutrino masses, finding that in general they apply not to the masses themselves, but only to related parameters, and they are numerically somewhat less stringent than has previously been claimed.