In-in formalism, pseudo-instantons and rethinking quantum cosmology

Understand

Unlike flat space quantum field theories that focus on scattering amplitudes, the main observables in quantum cosmology are correlation functions.

• The systematic way of calculating correlators is called in-in formalism, which requires only a single asymptotic region, i.e.
• past infinity.
• The rules in perturbation theory and the path integral measure are very different for in-in and in-out formalisms, and thus the results which are standard in one approach may not necessarily hold in the other one.