Effective theory for the cosmological generation of structure

TL;DR

This paper develops an effective framework coupling quantum matter to a dynamic gravitational background, incorporating back-reaction effects to better understand the quantum origins of cosmic structure formation.

Contribution

It introduces a novel effective theory that includes back-reaction of quantum fluctuations on the gravitational background, advancing the modeling of early universe structure formation.

Findings

Potential reduction in CMB power amplitude

Emergence of small non-Gaussianities

Suppression of large-scale odd mode power

Abstract

The current understanding of structure formation in the early universe is mainly built on a magnification of quantum fluctuations in an initial vacuum state during an early phase of accelerated universe expansion. One usually describes this process by solving equations for a quantum state of matter on a given expanding background space-time, followed by decoherence arguments for the emergence of classical inhomogeneities from the quantum fluctuations. Here, we formulate the coupling of quantum matter fields to a dynamical gravitational background in an effective framework which allows the inclusion of back-reaction effects. It is shown how quantum fluctuations couple to classical inhomogeneities and can thus manage to generate cosmic structure in an evolving background. Several specific effects follow from a qualitative analysis of the back-reaction, including a likely reduction of the overall amplitude of power in the cosmic microwave background, the occurrence of small non-Gaussianities, and a possible suppression of power for odd modes on large scales without parity violation.