Presents a functional approach to the construction, use and approximation of Green's functions and their associated ordered exponentials. It discusses new solut... » 

Presents a functional approach to the construction, use and approximation of Green's functions and their associated ordered exponentials. It discusses new solutions to problems involving particle production in crossed laser fields and non-constant electric fields. It also presents a variant of the Fadkin representation. In addition, it deals with adiabatic and stochastic approximations to unitary ordered exponentials. «