Frozen formalism and canonical quantization in group field theory
arXiv:2105.01100 · doi:10.1103/PhysRevD.104.106011
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.
17 pages, revtex two-column style; v2: extended discussion, minor typographical changes, updated references; version accepted in Physical Review D; v3: corrected a few typos, changed title to match journal publication title
References in corpus (8)
- Gravity quantized
- An effective approach to the problem of time
- Are the spectra of geometrical operators in Loop Quantum Gravity really discrete?
- Singularity resolution depends on the clock
- Unitarity, clock dependence and quantum recollapse in quantum cosmology
- Uniform discretizations: a new approach for the quantization of totally constrained systems
- Multiple choices of time in quantum cosmology
- Thermal representations in group field theory: squeezed vacua and quantum gravity condensates