Cosmology from Group Field Theory Formalism for Quantum Gravity

TL;DR

This paper derives a new effective cosmological model from group field theory quantum gravity, showing how macroscopic homogeneous geometries and modified Friedmann equations emerge from fundamental quantum dynamics.

Contribution

It introduces a method to extract cosmological dynamics from GFT, linking quantum gravity to effective classical cosmology.

Findings

Derivation of a non-linear, non-local quantum cosmology extension.

Identification of condensate states representing homogeneous geometries.

Modified Friedmann equations from GFT models with Laplacian kinetic terms.

Abstract

We identify a class of condensate states in the group field theory (GFT) approach to quantum gravity that can be interpreted as macroscopic homogeneous spatial geometries. We then extract the dynamics of such condensate states directly from the fundamental quantum GFT dynamics, following the procedure used in ordinary quantum fluids. The effective dynamics is a non-linear and non-local extension of quantum cosmology. We also show that any GFT model with a kinetic term of Laplacian type gives rise, in a semi-classical (WKB) approximation and in the isotropic case, to a modified Friedmann equation. This is the first concrete, general procedure for extracting an effective cosmological dynamics directly from a fundamental theory of quantum geometry.