Effective field theory and non-Gaussianity from general inflationary states

TL;DR

This work fuses Cheung et al.'s effective field theory of inflation with a general initial quantum state by encoding the initial density matrix into a boundary action and applying in-in perturbation theory. It demonstrates that the squeezed-limit consistency condition for the bispectrum can be violated by non-Bunch-Davies initial states, especially when the sound speed differs from unity, and quantifies how backreaction, tadpoles, and the power spectrum constrain such states. The authors compute the bispectrum for Gaussian and non-Gaussian initial states at leading and next-to-leading order in slow-roll, revealing potential large enhancements in squeezed and flattened configurations and highlighting how initial-state non-Gaussianity can modify local non-Gaussian signals. They show that EFT validity imposes a finite window, roughly Delta N \\sim \\ln(\\Lambda_* / H), within which initial-state effects can influence observables, and discuss implications for halo bias and future observational tests.

Abstract

We study the effects of non-trivial initial quantum states for inflationary fluctuations within the context of the effective field theory for inflation constructed by Cheung et al. which allows us to discriminate between different initial states in a model-independent way. We develop a Green's function/path integral based formulation that incorporates initial state effects and use it to address questions such as how state-dependent is the consistency relation for the bispectrum, how many e-folds beyond the minimum required to solve the cosmological fine tunings of the big bang are we allowed so that some information from the initial state survives until late times, among others. We find that the so-called consistency condition relating the local limit of the bispectrum and the slow-roll parameter is a state-dependent statement that can be avoided for physically consistent initial states either with or without initial non-Gaussianities.