FERMIONS COUPLED TO INSTANTONS IN 2 DIMENSIONS

We solve the problem of fermions interacting with instantons in two dimensions by using perturbation theory for the fermion sector. For massless fermions our solution is exact. We find that vacuum tunneling for a finite time interval in the presence of massless fermions is nonzero. As the time interval goes to infinity, vacuum tunneling is suppressed. We show that the fermions of the theory remain mas'sless to all orders of perturbation theory in the fermion sector, even though the correct vacuums are used. © 1979 The American Physical Society.