Enhanced Non-Gaussianity from Excited Initial States

TL;DR

This paper investigates how excited initial states during inflation can significantly enhance the CMB bi-spectrum, revealing potential observable signatures that differ from standard predictions, using effective field theory techniques.

Contribution

It introduces a framework to analyze excited inflationary initial states and demonstrates their potential to produce larger bi-spectrum signals than standard models.

Findings

Enhanced bi-spectrum for certain momentum configurations

Potential observability in current and future CMB data

Distinctive signatures in $l$-space for flattened triangles

Abstract

We use the techniques of effective field theory in an expanding universe to examine the effect of choosing an excited inflationary initial state built over the Bunch-Davies state on the CMB bi-spectrum. We find that even for Hadamard states, there are unexpected enhancements in the bi-spectrum for certain configurations in momentum space due to interactions of modes in the early stages of inflation. These enhancements can be parametrically larger than the standard ones and are potentially observable in current and future data. These initial state effects have a characteristic signature in $l$-space which distinguishes them from the usual contributions, with the enhancement being most pronounced for configurations corresponding to flattened triangles for which two momenta are collinear.