Fake instability in the Euclidean formalism of quantum tunneling

The Euclidean path-integral formalism is studied for the system without any unstable state. While the usual bounce calculation yields a fake complex energy spectrum, proper account of the global structure of the functional space is shown to lead to the real eigenvalues. For this purpose, the valley instanton is constructed by the proper valley method and the dilute-gas approximation is carried out. This establishes a general imaginary-time formalism, unifying the instanton and the bounce method.