Semiclassical scattering of quantized nonlinear waves

The relation between semiclassical phase shift and time delay, familiar from quantum mechanics, is extended to quantum field theory. This provides a semiclassical description for the scattering of quantized nonlinear waves. After a study of Levinson's theorem, our methods are applied to the sine-Gordon theory and the nature of the forces arising here is discussed. Finally, a covariant perturbative expansion for the one-particle sector is derived.