Solitosynthesis: Cosmological evolution of nontopological solitons.

Abstract

We consider the thermal creation, fusion, evaporation, and destruction of nontopological solitons (NTS's) after a phase transition in the early Universe. By defining and following NTS statistical equilibrium and departures from it, we show that depending on particle-physics parameters one of three possible scenarios occurs. If reaction rates are high enough, a period of equilibrium occurs and relic abundances are determined by the ``freeze-out'' temperature. We show that equilibrium first drives most NTS's into their constituents (free \ensuremath{\varphi} particles) and then causes rapid fusion into large NTS's. If freeze-out occurs during the first phase, the NTS's are almost entirely destroyed, while if it occurs during the second phase, solitosynthesis occurs and NTS's may be cosmically relevant. For slow reaction rates the NTS's are ``born frozen out'' and have the abundance determined by the phase transition. We develop analytic approximations for determining the abundances and test them by numerically integrating a reaction network in an expanding Universe. Unfortunately, for most of the parameter space considered, solitodestruction and/or evaporation occurs.