Nonlocal Quantum Gravity and the Size of the Universe

TL;DR

This paper investigates how nonlocal quantum effects in gravity can naturally lead to a very large, almost flat universe without fine-tuning the cosmological constant, by analyzing the renormalization group flow of nonlocal actions.

Contribution

It introduces a novel approach using the exact flow equation of Quantum Einstein Gravity to study nonlocal effective actions and their impact on the cosmological constant problem.

Findings

Renormalization group flow suppresses the curvature value from Planck-scale parameters.

Discovery of a critical infrared fixed point with scale-invariant gravity.

Large, nearly flat universes emerge without fine-tuning the cosmological constant.

Abstract

Motivated by the conjecture that the cosmological constant problem is solved by strong quantum effects in the infrared we use the exact flow equation of Quantum Einstein Gravity to determine the renormalization group behavior of a class of nonlocal effective actions. They consist of the Einstein-Hilbert term and a general nonlinear function $F_k(V)$ of the Euclidean spacetime volume $V$. For the $V + V \ln V$-invariant the renormalization group running enormously suppresses the value of the renormalized curvature which results from Planck-size parameters specified at the Planck scale. One obtains very large, i.e., almost flat universes without finetuning the cosmological constant. A critical infrared fixed point is found where gravity is scale invariant.