Extension of Loop Quantum Gravity to Metric Theories beyond General Relativity

TL;DR

This paper extends Loop Quantum Gravity's background-independent quantization method to a broad class of metric theories beyond General Relativity, including $f(R)$ and Brans-Dicke theories, using connection-dynamical formalism.

Contribution

It demonstrates how to reformulate $f(R)$ and Brans-Dicke theories into connection-dynamical formalism suitable for loop quantization, broadening the applicability of Loop Quantum Gravity.

Findings

Extended loop quantization to $f(R)$ theories

Reformulated Brans-Dicke theory in connection formalism

Outlined nonperturbative quantization procedure

Abstract

The successful background-independent quantization of Loop Quantum Gravity relies on the key observation that classical General Relativity can be cast into the connection-dynamical formalism with the structure group of SU(2). Due to this particular formalism, Loop Quantum Gravity was generally considered as a quantization scheme that applies only to General Relativity. However, we will show that the nonperturbative quantization procedure of Loop Quantum Gravity can be extended to a rather general class of metric theories of gravity, which have received increased attention recently due to motivations coming form cosmology and astrophysics. In particular, we will first introduce how to reformulate the 4-dimensional metric $f(R)$ theories of gravity, as well as Brans-Dicke theory, into connection-dynamical formalism with real SU(2) connections as configuration variables. Through these formalisms, we then outline the nonpertubative canonical quantization of the $f(R)$ theories and Brans-Dicke theory by extending the loop quantization scheme of General Relativity.