Group-Theoretical Quantization of 2+1 Geavity in the Metric-Torus Sector

TL;DR

This paper presents a symmetry-based quantization method for 2+1 gravity in the metric-torus sector, addressing algebraic and symmetry challenges to produce a consistent quantum theory.

Contribution

It introduces a group-theoretical quantization approach applicable to reparametrization invariant systems with closed Lie algebras, specifically applied to 2+1 gravity in the metric-torus sector.

Findings

Constructed a quantum theory with Hilbert space and observables.

Resolved algebraic closure issues via group completion.

Achieved a unique physical representation of the algebra.

Abstract

A symmetry based quantization method of reparametrization invariant systems is described; it will work for all systems that possess complete sets of perennials whose Lie algebras close and which generate a sufficiently large symmetry groups. The construction leads to a quantum theory including a Hilbert space, a complete system of operator observables and a unitary time evolution. The method is applied to the 2+1 gravity. The paper is restricted to the metric-torus sector, zero cosmological constant $\Lambda$ and it makes strong use of the so-called homogeneous gauge; the chosen algebra of perennials is that due to Martin. Two frequent problems are tackled. First, the Lie algebra of perennials does not generate a group of symmetries. The notion of group completion of a reparametrization invariant system is introduced so that the group does act; the group completion of the physical phase space of our model is shown to add only some limit points to it so that the ranges of observables are not unduly changed. Second, a relatively large number of relations between observables exists; they are transferred to the quantum theory by the well-known methods due to Kostant and Kirillov. In this way, a uniqueness of the physical representation of some extension of Martin's algebra is shown. The Hamiltonian is defined by a systematic procedure due to Dirac; for the torus sector, the result coincides with that by Moncrief. The construction may be extensible to higher genera and non-zero $\Lambda$ of the 2+1 gravity, because some complete sets of perennials are well-known and there are no obstructions to the closure of the algebra.