Abstract
We study scenarios in which the baryon asymmetry is generated from the decay of a particle whose mass originates from the spontaneous breakdown of a symmetry. This is realized in many models, including low-scale leptogenesis and theories with classical scale invariance. Symmetry breaking in the early universe proceeds through a phase transition that gives the parent particle a time-dependent mass, which provides an additional departure from thermal equilibrium that could modify the efficiency of baryogenesis from out-of-equilibrium decays. We characterize the effects of various types of phase transitions and show that an enhancement in the baryon asymmetry from decays is possible if the phase transition is of the second order, although such models are typically fine-tuned. We also stress the role of new annihilation modes that deplete the parent particle abundance in models realizing such a phase transition, reducing the efficacy of baryogenesis. A proper treatment of baryogenesis in such models therefore requires the inclusion of the effects we study in this paper.
Highlights
The Standard Model (SM) contains many fields but only one dimensionful parameter, since the symmetries of the theory forbid all such terms apart from the Higgs field mass
The fine-tuning that we find in the scalar potential points to the challenge of realizing a phase transition that proceeds in the adiabatic manner used in section 3 without either occurring too early or else producing a barrier between vacua leading to a first-order phase transition
We have systematically studied the effects of a phase transition on the baryon asymmetry generated via out-of-equilibrium decays
Summary
The Standard Model (SM) contains many fields but only one dimensionful parameter, since the symmetries of the theory forbid all such terms apart from the Higgs field mass. Outside of the realm of leptogenesis from decays, other studies of cosmological implications of dynamical masses have examined, for example, leptogenesis from interactions with the bubble wall of a first-order CP -violating phase transition [33], leptogenesis in a manner akin to electroweak baryogenesis [34,35,36], leptogenesis from the non-thermal production of right-handed neutrinos in bubble-wall collisions [37], as well as the effects of a phase transition on dark matter [38] and on cosmological implications of flavour models [39] Common to these studies, as well as our own, is the fact that the properties of particles can be very different in the early universe from the present day, and care should be exercised in interpreting and motivating experimental particle searches for such phenomena.
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