Vacuum tunneling in the four-dimensional Ising model

In the broken phase of the four-dimensional Ising model tunneling between the two degenerate minima of the effective potential takes place in a finite volume. We study this phenomenon numerically. The energies of the lowest zero momentum states are determined on both sides of the phase transition and their different correspondence to particle states in the infinite-volume limit is discussed. A Z2-invariant definition of the field expectation value and susceptibility is exploited for calculation of these quantities in finite volumes. (orig.)