Inflation with General Initial Conditions for Scalar Perturbations

TL;DR

The paper investigates whether general initial states for single-field inflationary fluctuations can be consistent with observational data, challenging the default BD vacuum assumption by analyzing coherent and broader excited states built on BD.It computes the power spectrum and bispectrum for coherent states and finds many such states yield BD-like results, with renormalization constraints further restricting high-momentum content.For general initial states, observational constraints on the power spectrum and local non-Gaussianity remain weak in quasi-de Sitter inflation, while adiabatic renormalization imposes nontrivial limitations on possible excitations, leading to a robust conclusion that many states are viable.Overall, the work shows that initial-state ambiguity may persist without conflicting with current data, while higher-point functions and renormalization provide promising avenues to probe pre-inflationary physics and motivate future observations.

Abstract

We explore the possibility of a single field quasi-de Sitter inflationary model with general initial state for primordial fluctuations. In this paper, first we compute the power spectrum and the bispectrum of scalar perturbations with coherent state as the initial state. We find that a large class of coherent states are indistinguishable from the Bunch-Davies vacuum state and hence consistent with the current observations. In case of a more general initial state built over Bunch-Davies vacuum state, we show that the constraints on the initial state from observed power spectrum and local bispectrum are relatively weak and for quasi-de Sitter inflation a large number of initial states are consistent with the current observations. However, renormalizability of the energy-momentum tensor of the fluctuations constraints the initial state further.