The fate of the B ball

The gauge-mediated SUSY-breaking (GMSB) model needs entropy production at a relatively low temperature in the thermal history of the Universe for the unwanted relics to be diluted. This requires a mechanism for the baryogenesis after the entropy production, and the Aeck and Dine (AD) mechanism is a promising candidate for it. The AD baryogenesis in the GMSB model predicts the existence of the baryonic Q ball, that is the B ball, and this may work as the dark matter in the Universe. In this article, we discuss the stability of the B ball in th presence of baryon-number violating interactions. We nd that the evaporation rate increases monotonically with the B-ball charge because the large eld value inside the B ball enhances the eect of the baryon-number-violating operators. While there are some diculties to evaluate the evaporation rate of the B ball, we derive the evaporation time (lifetime) of the B ball for the mass-to-charge ratio !0 > 100 MeV. The lifetime of the B ball and the distortion of the cosmic ray positron flux and the cosmic background radiation from the B ball evaporation give constraints on the baryon number of the B ball and the interaction, if the B ball is the dark matter. We also discuss some unresolved properties of the B ball.