In-In EFT

A bstract The effective field theory (EFT) construction when the objects of interest are the In-In (or real time) correlators rather than the In-Out S-matrix elements is constructed. This is done using the formal equivalence between the In-In and In-Out correlation functions, and demanding that the EFT and the full theory provide the same answers for the In-In correlation functions. Matching coefficients for a simple example are provided including for operators with two or more space or time derivatives. It is also pointed out that the Schroedinger representation of QFT captures some of the desired features of these calculations in a natural way and may actually serve as a link between these calculations and the broader amplitude programme.