On the large-scale structure of the inflationary universe

TL;DR

This paper investigates quantum fluctuations of a scalar field in an inflationary universe, deriving their spectrum and showing they do not induce non-perturbative or stochastic effects on spacetime evolution.

Contribution

It provides a new derivation of the intrinsic perturbation spectrum considering coupled scalar field and geometry, challenging previous fixed-background assumptions.

Findings

Intrinsic degrees of freedom are well-behaved in the infra-red spectrum.

Quantum fluctuations do not alter the perturbative nature of spacetime evolution.

The derived spectrum contradicts earlier fixed-background results.

Abstract

We study the evolution of quantum fluctuations of a scalar field which is coupled to the geometry, in an exponentially expanding universe. We derive an expression for the spectrum of intrinsic perturbations, and it is shown that the intrinsic degrees of freedom are well behaved in the infra-red part of the spectrum. We conclude that quantum fluctuations do not change the dynamics of the spacetime in a way which makes its evolution non-perturbative and stochastic. This result contradicts previous derivations which are based on the study of a quantum field on a fixed geometry.