False vacuum decay with gravity in the non-thin-wall limit - art. no. 103508

We consider a wave-function approach to the false vacuum decay with gravity and present a new method to calculate the tunneling amplitude under the WK B approximation. The result agrees with the one obtained by the Euclidean p ath-integral method, but gives a much clearer interpretation of an instanto n (Euclidean bounce solution) that dominates the path integral. In particul ar, our method is fully capable of dealing with the case of a thick wall wi th the radius of the bubble comparable to the radius of the instanton, thus surpassing the path-integral method whose use can be justified only in the thin-wall and small bubble radius limit. The calculation is done by matchi ng two WKB wave functions, one with the final state and another with the in itial state, with the wave function in the region where the scale factor of the metric is sufficiently small compared with the inverse of the typical energy scale of the field potential at the tunneling. The relation of the b oundary condition on our wave function for the false vacuum decay with the Hartle-Hawking no-boundary boundary condition and Vilenkin's tunneling boun dary condition on the wave function of the universe is also discussed.