2+1 homogeneous Loop Quantum Gravity with a scalar field clock

TL;DR

This paper develops a three-dimensional quantum reduced loop gravity model with a scalar field, simplifying the scalar Hamiltonian operator and exploring its implications for understanding quantum cosmology.

Contribution

It introduces a simplified method for computing the scalar Hamiltonian in 3D QRLG with matter, linking reduced LQG to LQC and exploring matter coupling effects.

Findings

Derived matrix elements of the scalar Hamiltonian operator.

Established connections between 3D QRLG and LQC.

Discussed the role of the scalar field as a dynamical carrier.

Abstract

We focus on three-dimensional QRLG with the purpose of shedding light on the link between reduced LQG and LQC in four space-time dimensions. Considering homogeneous three-dimensional LQG, the theory simplifies to QRLG. We then implement Thiemann's Quantum Spin Dynamics for Euclidean three-dimensional space-time in presence of a real scalar matter field. We deploy a polymer quantization of the scalar field while using methods of quantum reduced loop gravity. We compute the scalar Hamiltonian operator on the states of the kinematical Hilbert space of the theory, and exhibit its matrix elements that are derived using a new simplified method. The coupling to matter, which plays the role of a carrier of dynamics, opens the pathway to the study of phenomenological implications. We finally comment on the relations between three-dimensional QRLG and LQC, as well as on the appearance of the correspondence principle for the scalar field.