Loop Quantum Gravity and the The Planck Regime of Cosmology

TL;DR

This paper discusses how loop quantum gravity extends cosmological models to include the Planck era, revealing potential observable effects like modified spectra and non-Gaussianities, thus connecting quantum gravity with early universe observations.

Contribution

It introduces a self-consistent loop quantum gravity framework that models the universe from the Planck regime to inflation, covering 11 orders of magnitude in curvature, and predicts novel observable effects.

Findings

Extension of inflationary paradigm to Planck era using loop quantum gravity

Potential modifications in scalar and tensor spectra due to quantum effects

Emergence of non-Gaussianities from quantum gravity fluctuations

Abstract

The very early universe provides the best arena we currently have to test quantum gravity theories. The success of the inflationary paradigm in accounting for the observed inhomogeneities in the cosmic microwave background already illustrates this point to a certain extent because the paradigm is based on quantum field theory on the curved cosmological space-times. However, this analysis excludes the Planck era because the background space-time satisfies Einstein's equations all the way back to the big bang singularity. Using techniques from loop quantum gravity, the paradigm has now been extended to a self-consistent theory from the Planck regime to the onset of inflation, covering some 11 orders of magnitude in curvature. In addition, for a narrow window of initial conditions, there are departures from the standard paradigm, with novel effects, such as a modification of the consistency relation involving the scalar and tensor power spectra and a new source for non-Gaussianities. Thus, the genesis of the large scale structure of the universe can be traced back to quantum gravity fluctuations \emph{in the Planck regime}. This report provides a bird's eye view of these developments for the general relativity community.