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WS21/22 – Abstract
Bianca Dittrich
(Perimeter, Waterloo)
9.12.2021
Exploring Lorentzian quantum gravity via effective spin foams
Spin foams are a non-perturbative approach to construct path integrals for Lorentzian space times, based on a precise notion of quantum geometry. This notion of quantum geometry has some surprising aspects: an anomaly in the constraint algebra forces the inclusion of non-metric degrees of freedom. This has put into question whether spin foams do lead, in the classical limit to the dynamics of general relativity.
Recently, effective spin foam models were introduced, which greatly enhanced numerical accessibility and understanding of the dynamics of spin foams. This allowed us to identify mechanisms which overcome the problems resulting from the anomaly . I will report on this recent progress, facilitated by the effective models, and on the new understanding of the semi-classical dynamics and continuum limit of spin foam models. I will then discuss some features for the Lorentzian path integral, e.g. imposition of causality, which can now be explicitly explored with the effective spin foams, and sketch applications to cosmology.
