Alternate Definitions of Loop Corrections to the Primordial Power Spectra

TL;DR

This paper compares two different methods for defining loop corrections to the primordial power spectra, showing they agree at tree level but differ at one loop, highlighting the ambiguity in higher-order corrections.

Contribution

It introduces and contrasts two definitions of loop corrections to primordial power spectra, analyzing their differences at the one-loop level.

Findings

The two definitions agree at tree order.

They disagree at one loop using Schwinger-Keldysh formalism.

Discussion of the advantages and disadvantages of each method.

Abstract

We consider two different definitions for loop corrections to the primordial power spectra. One of these is to simply correct the mode functions in the tree order relations using the linearized effective field equations. The second definition involves the spatial Fourier transform of the 2-point correlator. Although the two definitions agree at tree order, we show that they disagree at one loop using the Schwinger-Keldysh formalism, so there are at least two plausible ways of loop correcting the tree order result. We discuss the advantages and disadvantages of each.