Phase transitions precipitated by solitosynthesis

Solitosynthesis of Q-balls in the false vacuum can result in a phase transition of a new kind. Formation and subsequent growth of Q-balls via the charge accretion proceeds until the solitons reach a critical charge, at which point it becomes energetically favorable for the Q-ball interior to expand filling space with the true vacuum phase. Solitosynthesis can destabilize a false vacuum even when the tunneling rate is negligible. In models with low-energy supersymmetry, where the Q-balls associated with baryon and lepton number conservation are generically present, solitosynthesis can precipitate transitions between the vacua with different VEV’s of squarks and sleptons. CERN-TH/97-106 May, 1997 ∗ email address: [email protected] A variety of models, in particular the supersymmetric generalizations of the Standard Model (SSM), possess non-topological solitons of the Q-ball type in their spectrum [1]. Their existence and stability is due to some conserved charge associated with a global U(1) symmetry, e. g., baryon (B) or lepton (L) number. In the early Universe, Q-balls can be created [2] in the course of a phase transition (“solitogenesis”), or they can be produced via fusion [3, 4] in a process reminiscent of the big bang nucleosynthesis (“solitosynthesis”). Finally, small Q-beads [5] can be pair-produced at high temperature. In the false vacuum, Q-balls can have a negative energy density in their interior if there is a lower U(1)-breaking minimum in the potential, or, more generally, whenever the scalar potential is negative for some value of a charged field. When the charge of such Q-ball reaches a critical value, it becomes energetically favorable for the soliton interior to expand filling the Universe with the “true vacuum” phase. A first-order phase transition facilitated by a criticalsize Q-ball differs from tunneling in that (i) the “critical bubble” of the true vacuum is charged and has different symmetries from those of the usual “bounce”; and, most importantly, (ii) the critical Q-ball can build up gradually via the charge accretion. The role of charge conservation is to stabilize the sub-critical Q-balls and prevent them from collapsing while they grow in size gradually until their charge reaches the critical value Qc. This allows for a new type of a phase transition, that precipitated by solitosynthesis. This type of a phase transition is different from that previously discussed in the literature [6, 7, 8], where the Q-balls form at high temperature, before the vacuum becomes metastable, and grow in size slowly as the temperature decreases because of the changes in the temperaturedependent effective potential. In this letter we consider solitosynthesis that takes place at relatively low temperatures in the false vacuum whose lifetime can be large on the cosmological time scale. When a Q-ball reaches a critical size Qc > ∼ 10 , it can facilitate a first-order phase transition which would otherwise never take place during the lifetime of the Universe because the probability of tunneling is too small. Copious production of critical Q-balls is possible if a chain of reactions that leads from individual particles to the critical-size solitons remains in thermal equilibrium. A freeze-out of any one of these processes can stymie the solitosynthesis. It is, therefore, important that,