Signature change in loop quantum gravity: General midisuperspace models and dilaton gravity

TL;DR

This paper investigates how loop quantum gravity models exhibit signature change due to deformed covariance, confirmed across various midisuperspace models and dilaton gravity theories with holonomy modifications.

Contribution

It provides a general analysis of signature change in all midisuperspace models without local degrees of freedom, extending previous results to a broader class of theories.

Findings

Signature change occurs in models with holonomy modifications.

Classical dilaton gravity models do not show deformed covariance.

Deformed covariance is linked to anomaly freedom conditions.

Abstract

Models of loop quantum gravity based on real connections have a deformed notion of general covariance, which leads to the phenomenon of signature change. This result is confirmed here in a general analysis of all midisuperspace models without local degrees of freedom. As a subclass of models, 2-dimensional theories of dilaton gravity appear, but a larger set of examples is possible based only on the condition of anomaly freedom. While the classical dilaton gravity models are the only such systems without deformed covariance, they do give rise to signature change when holonomy modifications are included.