Loop quantum gravity, signature change, and the no-boundary proposal

TL;DR

This paper explores how loop quantum gravity predicts signature change at high densities and demonstrates how this affects quantum cosmology proposals, resolving instabilities and relaxing density constraints.

Contribution

It provides detailed derivations showing the interplay of signature change with quantum cosmology proposals, highlighting the resolution of instabilities and density conditions.

Findings

Signature change occurs at high densities in loop quantum gravity.

Instabilities in inhomogeneous perturbations are naturally cured.

Dynamical signature change does not require Planckian densities off-shell.

Abstract

Covariant models of loop quantum gravity generically imply dynamical signature change at high density. This article presents detailed derivations that show the fruitful interplay of this new kind of signature change with wave-function proposals of quantum cosmology, such as the no-boundary and tunneling proposals. In particular, instabilities of inhomogeneous perturbations found in a Lorentzian path-integral treatment are naturally cured. Importantly, dynamical signature change does not require Planckian densities when off-shell instantons are relevant.