Fermion Vacuum Effects on Soliton Stability

Just as fermion zero modes can alter the degeneracy and quantum numbers of a soliton, fermion energies can affect the form and stability of a nontopological soliton. We discuss the kink in a two-dimensional linear sigma model, and show that, when coupled to fermions, the kink is no longer an extremum of the energy functional. The kink in this model possesses many similarities to the electroweak string in the Weinberg-Salam model.