Effective potential and asymmetric instantons

Perturbing the double-well potential by a constant external source leads to instanton splitting and to unstable quantum modes. Nevertheless, it is shown that the effective potential is still dominated by instantonlike configurations which are only piecewise classical solutions having a countable number of energy discontinuities and asymmetrical asymptotic behaviour. They are determined by maximizing the number of zero modes while minimizing the tadpole contributions which are shown to yield higher-order corrections to the energy shift