Manifestly unitary cosmological perturbation theory

Abstract The next decade will feature an abundance of novel cosmological data, while many fundamental questions about inflation remain. Given this, there is ample need for maximally efficient calculations, especially in non-standard scenarios the early Universe. In inflationary cosmology, observables are computed within framework in-in perturbation theory. Weinberg introduced a now-widely used re-organization theory calculations. There subtle difference iϵ prescriptions Weinberg's series with traditional in-in, which could interfere projection onto interacting vacuum. this work, we show that small adjustment to yields agreement standard at every order commonly studied spins and masses de Sitter spacetime. We then generalize result large class spacetimes, including slow roll spacetimes.