Loop quantum cosmology with self-dual variables

TL;DR

This paper develops a loop quantum cosmology framework using self-dual variables, demonstrating how to impose reality conditions, defining suitable operators, and deriving effective equations that resolve classical singularities with a quantum bounce.

Contribution

It introduces a novel loop quantum cosmology formulation with self-dual variables, including a method to impose reality conditions and construct Hamiltonian operators, extending standard LQC.

Findings

Quantum effects resolve big-bang and big-crunch singularities.

Effective Friedmann equations approximate quantum dynamics well.

Self-dual variables lead to a non-singular bounce replacing classical singularities.

Abstract

Using the complex-valued self-dual connection variables, the loop quantum cosmology of a closed Friedmann universe coupled to a massless scalar field is studied. It is shown how the reality conditions can be imposed in the quantum theory by choosing a particular inner product for the kinematical Hilbert space. While holonomies of the self-dual Ashtekar connection are not well-defined in the kinematical Hilbert space, it is possible to introduce a family of generalized holonomy-like operators of which some are well-defined; these operators in turn are used in the definition of the Hamiltonian constraint operator where the scalar field can be used as a relational clock. The resulting quantum theory is closely related, although not identical, to standard loop quantum cosmology constructed from the Ashtekar-Barbero variables with a real Immirzi parameter. Effective Friedmann equations are derived, which provide a good approximation to the full quantum dynamics for sharply-peaked states whose volume remains much larger than the Planck volume, and they show that for these states quantum gravity effects resolve the big-bang and big-crunch singularities and replace them by a non-singular bounce. Finally, the loop quantization in self-dual variables of a flat Friedmann space-time is recovered in the limit of zero spatial curvature and is identical to the standard loop quantization in terms of the real-valued Ashtekar-Barbero variables.