Quantum cosmology of pure connection general relativity

TL;DR

This paper explores homogeneous cosmological models using a connection-based formulation of general relativity, analyzing classical dynamics, reality conditions, and quantum aspects, revealing signature ambiguities and simplifying cases.

Contribution

It introduces a detailed analysis of classical and quantum homogeneous cosmologies within a connection formulation, highlighting reality conditions and their impact on Lorentzian solutions.

Findings

Different reality condition branches lead to distinct real Hamiltonian theories.

The flat Bianchi I model simplifies the reality conditions and dynamics.

Quantum path integral reduces to a boundary term, reproducing known quantum cosmology results.

Abstract

We study homogeneous cosmological models in formulations of general relativity with cosmological constant based on a (complexified) connection rather than a spacetime metric, in particular in a first order theory obtained by integrating out the self-dual two-forms in the chiral Plebanski formulation. Classical dynamics for the Bianchi IX model are studied in the Lagrangian and Hamiltonian formalism, where we emphasise the reality conditions needed to obtain real Lorentzian solutions. The solutions to these reality conditions fall into different branches, which in turn lead to different real Hamiltonian theories, only one of which is the usual Lorentzian Bianchi IX model. We also show the simpler case of the flat Bianchi I model, for which both the reality conditions and dynamical equations simplify considerably. We discuss the relation of a real Euclidean version of the same theory to this complex theory. Finally, we study the quantum theory of homogeneous and isotropic models, for which the pure connection action for general relativity reduces to a pure boundary term and the path integral is evaluated immediately, reproducing known results in quantum cosmology. An intriguing aspect of these theories is that the signature of the effective spacetime metric, and hence the interpretation of the cosmological constant, are intrinsically ambiguous.