The effective field theory of the gravitational functional measure

TL;DR

This paper uses effective field theory to analyze the gravitational path integral measure, identifying a UV fixed point that justifies the standard DeWitt metric from fundamental principles.

Contribution

It introduces a configuration-space metric expanded by energy and studies its renormalization group flow, revealing a UV fixed point that supports the physical choice of the measure.

Findings

A flat configuration space is excluded by unitarity.

The renormalization group has a UV fixed point at λ = -1.

The fixed point justifies the standard DeWitt metric from first principles.

Abstract

The gravitational path integral measure has been the subject of an increasing interest lately, and no conclusive answer yet exists for its correct form. In this paper, we adopt effective field theory techniques to shed light on this issue. We build the configuration-space metric as an energy expansion, including all possible terms that satisfy the underlying symmetries, and use it to define a Riemannian measure. We study the running of the free parameters that show up in this expansion at leading order, which corresponds to the DeWitt metric with parameter $\lambda$. We show that a flat configuration space is excluded on unitarity grounds. The renormalization group contains one UV fixed point at $\lambda=-1$, thus allowing for the UV completion of the measure sector. This fixed point corresponds to the value obtained by identifying DeWitt's metric from the kinetic term of general relativity, a standard procedure in the literature that otherwise lacks physical motivation. Our results provide such a justification from first principles.