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We study the formation of Q balls which are made of flat directions that appear in the supersymmetric extension of the standard model in the context of gravity-mediated supersymmetry breaking. The full nonlinear calculations for the dynamics of the complex scalar field are made. Since the scalar potential in this model is flatter than ^2, we have found that fluctuations develop and go nonlinear to form nontopological solitons, Q balls. The size of a Q ball is determined by the most amplified mode, which is completely determined by the model parameters. On the other hand, the charge of Q balls depends linearly on the initial charge density of the Affleck-Dine (AD) field. Almost all the charges are absorbed into Q balls, and only a tiny fraction of the charges is carried by a relic AD field. It may lead to some constraints on the baryogenesis and/or parameters in the particle theory. The peculiarity of gravity mediation is the moving Q balls. This results in collisions between Q balls. It may increase the charge of the Q balls, and change its fate.
Kasuya et al. (Fri,) studied this question.