Singlet Majoron model with hidden scale invariance

We investigate an extension of the singlet Majoron model in which the breaking of dilatation symmetry by the mass parameters of the scalar potential is removed by means of a dilaton field. Starting from the one-loop renormalization group improved potential, we discuss the ground state of the theory. The flat direction in the classical potential is lifted by quantum corrections and the true vacua are found. Studying the finite temperature potential, we analyze the cosmological consequences of a Jordan-Brans-Dicke dilaton and show that the lepton number is spontaneously broken after the electroweak phase transition, thus avoiding any constraint coming from the requirement of the preservation of the baryon asymmetry in the early Universe. We also find that, contrary to the standard model case, the dilaton and/or neutrino cosmology do not impose any upper bound on the scale of the spontaneous breaking of scale invariance if the τ neutrino is sufficiently heavy