Nonconservation of the fermion number in the decay of a heavy fermion in a two-dimensional gauge model

It is shown in the framework of $U(1)$ gauge model in $(1+1)$ dimensions that the effects of the composite structure of vacuum imply the unstability of the lowest state with the non-zero fermion number (the state represents a nontopological soliton). In the semiclassical approximation critical values of parameters of the model are found at which the nontopological soliton becomes unstable with respect to rapid anomalous decay with fermion number nonconservation.