Non-Gaussianity from Excited Initial Inflationary States

TL;DR

This paper investigates how excited initial states during inflation can generate observable non-Gaussianity, finding that most states do not produce detectable signals unless specific conditions are met.

Contribution

It provides a model-independent analysis of excited initial states' impact on non-Gaussianity, identifying conditions under which observable signals may arise.

Findings

Most excited states do not produce observable $f_{NL}$

A specific excited state configuration can generate detectable $f_{NL}$

Constraints on initial states ensure compatibility with observed power spectrum

Abstract

We study squeezed limit $f_{NL}$ generation by excited initial inflationary states in a model independent way. We restrict "excited" to mean a Bogoliubov transformation of the Bunch Davies state. We simultaneously impose the constraints that the observable power spectrum is nearly scale invariant over at least three decades and that the observable modes today be subhorizon at the beginning of inflation while not causing significant backreaction. We show that most excited initial inflationary states for single field inflationary models with negligible superhorizon evolution do not produce an observable squeezed limit $f_{NL}$. The case in which one mode is in the Bunch Davies state while the other two modes are in an excited state with $0.01<|\beta_k|\leq0.1$ may generate a squeezed limit $f_{NL}$ which is detectable with future experiments.