Dynamical Dark Energy from Lattice Quantum Gravity

TL;DR

This paper investigates how quantum gravity effects from lattice simulations suggest a dynamical dark energy model with a running cosmological constant, potentially explaining the universe's accelerated expansion with testable deviations from standard cosmology.

Contribution

It introduces a lattice quantum gravity approach that reveals a scale-dependent cosmological constant, providing a novel quantum gravity-based model for dark energy.

Findings

The vacuum geometry aligns with de Sitter space but shows deviations indicating non-trivial vacuum dynamics.

The cosmological constant runs quadratically with scale, linked to the Hubble rate.

Predicted deviations from ΛCDM are at the 10^{-3} level, testable with future observations.

Abstract

We study the behavior of the vacuum in Euclidean dynamical triangulations (EDT). Algorithmic improvements and better lattice spacing determinations allow us to test the properties of the emergent de Sitter geometries of our simulations to higher precision than previously possible. Although the agreement with de Sitter is good, the improved precision reveals deviations that can be interpreted as non-trivial vacuum dynamics, well-described by a cosmological constant that runs with scale. The simulations show that the dominant running is quadratic and that the scale can be identified with the Hubble rate. Several key cross-checks support this picture, including consistent results across multiple lattice spacings and the fact that the null energy condition is not violated. The parameters of the running are fully determined by simulations, enabling predictions when extrapolated to the scales relevant for our universe. This leads to a model for dark energy that is compatible with current observations, but which predicts deviations from $\Lambda$CDM at the ${\cal O}(10^{-3})$ level in cosmological observables that could be tested with future improvements in precision measurements.