Towards the physical vacuum of cosmic inflation

There have been long debates about the initial conditions of inflationary perturbations. In this work we explicitly show the decay of excited states during inflation via interactions from the renormalization group point of view. For this purpose, we note that the folded shape non-Gaussianity can be interpreted as the decay of the non-Bunch-Davies initial condition. The one loop diagrams with non-Bunch-Davies propagators are calculated to uncover the decay of such excited states. We find that the decay of amplitude is contributed by the folded shape of loop momentum and is irrelevant to the UV part. The conformal decay rate is related to the strength of non-Gaussianity via Gamma similar to (f(NL)(lambda))(2) P(zeta)k(5)O(tau(4) , tau(4)(0)). The observed smallness of non-Gaussianity keeps the window open for probing inflationary initial conditions and trans-Planckian physics. (C) 2016 The Author(s). Published by Elsevier B.V.