Signature change in loop quantum gravity: Two-dimensional midisuperspace models and dilaton gravity

摘要

Models of loop quantum gravity based on real connections have a deformed notion of generalcovariance, which leads to the phenomenon of signature change. This result is confirmed here in a generalanalysis of all midisuperspace models without local degrees of freedom. As a subclass of models, twodimensionaltheories of dilaton gravity appear, but a larger set of examples is possible based only on thecondition of anomaly freedom. While the classical dilaton gravity models are the only such systemswithout deformed covariance, they do give rise to signature change when holonomy modifications areincluded.