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

摘要

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