Talks by Bianca Dittrich

Space and Time in a Lorentzian path integral

Bianca Dittrich Perimeter Institute for Theoretical Physics
I will present a quantum gravity approach based on a Lorentzian path integral for quantum geometries. The properties of quantum space time can be measured using geometric operators. This allows also to discuss fluctuations of causal structure as well as violations of (micro-) causality. I will explain how the Lorentzian path integral comes with various options regarding which quantum space times to sum over: e.g. whether to include causality violations or not, or whether to allow also for space times with Euclidean signatures in Lorentzian path integrals.

Towards Lorentzian quantum gravity via effective spin foams

Bianca Dittrich Perimeter Institute for Theoretical Physics

Euclidean quantum gravity approaches have a long history but suffer from a number of severe issues.  This gives a strong motivation to develop Lorentzian approaches. Spin foams constitute an important such approach, which incorporate a rigorously derived discrete area spectrum.  I will explain how this discrete area spectrum is connected to the appearance of an anomaly, which explains the significance of the Barbero-Immirzi parameter and forces an extension of the quantum configuration space, to also include torsion degrees of freedom.

Tensor network description of 3D Quantum Gravity and Diffeomorphism Symmetry

Bianca Dittrich Perimeter Institute for Theoretical Physics
In contrast to the 4D case, there are well understood theories of quantum gravity for the 3D case. Indeed, 3D general relativity constitutes a topological field theory (of BF or equivalently Chern-Simons type) and can be quantized as such. The resulting quantum theory of gravity offers many interesting lessons for the 4D case. In this talk I will discuss the quantum theory which results from quantizing 3D gravity as a topological field theory. This will also allow a derivation of a holographic boundary theory, together with a geometric interpretation of the boundary observables.

Quantum Geometry vs. Quantum Gravity

Bianca Dittrich Perimeter Institute for Theoretical Physics

Quantizing 4D geometries leads to discrete area spectra. Such discrete area spectra are also suggested by the holographic principle and entropy counting for black holes.