On unimodular quantum gravity

TL;DR

This paper demonstrates the existence of a non-trivial ultraviolet fixed point in unimodular quantum gravity, suggesting it can be a consistent quantum theory distinct from standard Einstein gravity, with unique renormalization properties.

Contribution

It identifies a UV fixed point in unimodular quantum gravity and explores its differences from standard asymptotic safety scenarios, including new gauge-fixing approaches.

Findings

Existence of a non-trivial UV fixed point in unimodular gravity

Unimodular gravity's quantum properties differ from Einstein gravity

Evidence supporting unimodular gravity as a consistent quantum theory

Abstract

Unimodular gravity is classically equivalent to standard Einstein gravity, but differs when it comes to the quantum theory: The conformal factor is non-dynamical, and the gauge symmetry consists of transverse diffeomorphisms only. Furthermore, the cosmological constant is not renormalized. Thus the quantum theory is distinct from a quantization of standard Einstein gravity. Here we show that within a truncation of the full Renormalization Group flow of unimodular quantum gravity, there is a non-trivial ultraviolet-attractive fixed point, yielding a UV completion for unimodular gravity. We discuss important differences to the standard asymptotic-safety scenario for gravity, and provide further evidence for this scenario by investigating a new form of the gauge-fixing and ghost sector.