Testing the Master Constraint Programme for Loop Quantum Gravity I. General Framework

TL;DR

This paper introduces the general framework of the Master Constraint Programme in Loop Quantum Gravity, demonstrating its applicability across various models with different constraint algebra complexities, and developing an alternative solution method for quantum constraints.

Contribution

It provides the foundational framework for the Master Constraint Programme and develops the Direct Integral Decomposition method as an alternative to RAQ.

Findings

Successfully applied the Master Constraint Programme to diverse models

Identified subtleties in implementing the method for complex algebras

Developed the Direct Integral Decomposition as a new solution approach

Abstract

Recently the Master Constraint Programme for Loop Quantum Gravity (LQG) was proposed as a classically equivalent way to impose the infinite number of Wheeler -- DeWitt constraint equations in terms of a single Master Equation. While the proposal has some promising abstract features, it was until now barely tested in known models. In this series of five papers we fill this gap, thereby adding confidence to the proposal. We consider a wide range of models with increasingly more complicated constraint algebras, beginning with a finite dimensional, Abelean algebra of constraint operators which are linear in the momenta and ending with an infinite dimensional, non-Abelean algebra of constraint operators which closes with structure functions only and which are not even polynomial in the momenta. In all these models we apply the Master Constraint Programme successfully, however, the full flexibility of the method must be exploited in order to complete our task. This shows that the Master Constraint Programme has a wide range of applicability but that there are many, physically interesting subtleties that must be taken care of in doing so. In this first paper we prepare the analysis of our test models by outlining the general framework of the Master Constraint Programme. The models themselves will be studied in the remaining four papers. As a side result we develop the Direct Integral Decomposition (DID) for solving quantum constraints as an alternative to Refined Algebraic Quantization (RAQ).