Quantum gravity on finite spacetimes and dynamical mass

TL;DR

This paper reviews the development of quantum gravity models using quantum Riemannian geometry on finite and fuzzy spaces, highlighting new results like a Kaluza-Klein analysis with dynamically generated masses.

Contribution

It introduces a formalism for quantum Riemannian geometry on finite and noncommutative spaces, and presents new results including a Kaluza-Klein type analysis with scalar fields and masses.

Findings

Uniform nonzero variance of metric expectation values in strong gravity

Construction of quantum FLRW cosmology and black-hole backgrounds

Scalar fields with dynamically generated masses from finite quantum geometries

Abstract

We review quantum gravity model building using the new formalism of `quantum Riemannian geometry' to construct this on finite discrete spaces and on fuzzy ones such as matrix algebras. The formalism starts with a `differential structure' as a bimodule $\Omega^1$ of differential 1-forms over the coordinate algebra $A$, which could be noncommutative. A quantum metric is a noncommutative rank (0,2) tensor in $\Omega^1\otimes_A\Omega^1$, for which we then search for a quantum Levi-Civita connection (this is no longer unique or guaranteed). We outline the three models which have so far been constructed in this formalism, commonalities among them, and issues going forward. One commonality is a uniform nonzero variance of metric expectation values in the strong gravity limit. We also outline and discuss the construction of quantum FLRW cosmology and black-hole backgrounds using quantum Riemannian geometry and other recent results. Among new results, we perform a Kaluza-Klein type analysis where we tensor classical spacetime coordinates with a finite quantum Riemannian geometry and we give an example where a scalar field on the total space appears as a multiplet of scalar fields on spacetime with a spread of dynamically generated masses.