Quantum signatures and decoherence during inflation from deep subhorizon perturbations

In order to shed light on the quantum-to-classical transition of the primordial perturbations in single field inflation, we investigate the decoherence of large-scale (superhorizon) scalar curvature perturbations. The latter are considered as an open quantum system which undergoes quantum decoherence induced by a time-dependent environment of deep subhorizon tensorial modes through the trilinear interactions predicted by General Relativity. A complete calculation is a complex one and still to be fully performed. We advance in that direction, and we elaborate on various aspects that have been overlooked in the literature. We first prove that, in full generality, a time dependent subhorizon environment can be relevant for decoherence during inflation, by considering derivativeless interactions, which, in our case, give the most important results. For the first time, the time dependence of the environment is properly taken into account by modifying the quantum master equation. Important non-Markovian effects pop up, instead, when dealing with derivative interactions. We adopt a possible way to treat them which has been recently proposed and seems well suited for our case. Our results show that when considering the interplay between derivativeless and derivative interactions, decoherence is slowed down. This underlines the importance of accounting for all the interactions in open quantum-system calculations in an inflationary setting. We finally compute the quantum corrections to cosmological correlation functions, by solving the transport equations induced by the quantum master equation. We also compare the results to the solutions obtained by an alternative method previously used in the literature. We observe a resummation of the quantum corrections to the power-spectrum of the Sasaki Mukhanov variable v, which is a general property of quantum master equations. We extend these results to the bispectrum of v.