Frozen formalism and canonical quantization in group field theory

TL;DR

This paper introduces a frozen formalism and Dirac quantization approach for group field theory in quantum gravity, linking existing methods and enabling the construction of physical observables without a preferred time parameter.

Contribution

It develops a new frozen formalism for group field theory that unifies deparametrization and timeless quantization approaches in quantum gravity.

Findings

Equivalent to usual canonical quantization for scalar fields.

Links deparametrization and timeless approaches in group field theory.

Derives effective cosmological dynamics within the new formalism.

Abstract

Canonical quantization of gravitational systems is obstructed by the problem of time. Due to diffeomorphism symmetry the Hamiltonian vanishes: dynamics with respect to a background time parameter appears "frozen." Two strategies towards the quantization of such systems are the identification of a clock degree of freedom before quantization (deparametrization), and quantization on a kinematical Hilbert space which is subject to constraints (Dirac quantization). The usual canonical quantization in quantum field theory is analogous to deparametrization. Here we introduce a frozen formalism and Dirac quantization for a complex Klein-Gordon scalar field, and show that the resulting theory is equivalent to usual canonical quantization. We then apply the formalism to the group field theory formalism for quantum gravity, for which both deparametrization and a "timeless" quantization have been proposed in past work. We show how a frozen formalism for group field theory links between these two existing approaches, and illustrate in particular the construction of physical observables. We derive effective cosmological dynamics for group field theory in the new formalism and compare these to previous work. The frozen formalism could be extended to other approaches to quantum gravity that do not use a preferred time parameter.