Towards an Anomaly-Free Quantum Dynamics for a Weak Coupling Limit of Euclidean Gravity

TL;DR

This paper constructs an anomaly-free quantum Hamiltonian constraint for a U(1)^3 gauge theory derived from Euclidean gravity's G→0 limit, aiming to advance the quantum dynamics understanding in Loop Quantum Gravity.

Contribution

It develops a density weight 4/3 quantum Hamiltonian constraint that reproduces the classical Poisson brackets in a non-trivial LQG-type representation, addressing anomaly issues.

Findings

Finite triangulation operators reproduce classical constraints.

Continuum limit of commutators matches classical Poisson brackets.

Constructed operators generate generalized diffeomorphisms.

Abstract

The G -->0 limit of Euclidean gravity introduced by Smolin is described by a generally covariant U(1)xU(1)xU(1) gauge theory. The Poisson bracket algebra of its Hamiltonian and diffeomorphism constraints is isomorphic to that of gravity. Motivated by recent results in Parameterized Field Theory and by the search for an anomaly-free quantum dynamics for Loop Quantum Gravity (LQG), the quantum Hamiltonian constraint of density weight 4/3 for this U(1)xU(1)xU(1) theory is constructed so as to produce a non-trivial LQG-type representation of its Poisson brackets through the following steps. First, the constraint at finite triangulation, as well as the commutator between a pair of such constraints, are constructed as operators on the `charge' network basis. Next, the continuum limit of the commutator is evaluated with respect to an operator topology defined by a certain space of `vertex smooth' distributions. Finally, the operator corresponding to the Poisson bracket between a pair of Hamiltonian constraints is constructed at finite triangulation in such a way as to generate a `generalised' diffeomorphism and its continuum limit is shown to agree with that of the commutator between a pair of finite triangulation Hamiltonian constraints. Our results in conjunction with the recent work of Henderson, Laddha and Tomlin in a 2+1-dimensional context, constitute the necessary first steps toward a satisfactory treatment of the quantum dynamics of this model.