Teilchentee WS 2020

An old issue in (semi-classical) quantum gravity deals with the question which saddle points contribute in the Euclidean path integral. Especially when the topology of the saddle point is non-trivial rather striking effects on the effective field theory could take place such as a randomness of constants of nature. This has been studied in the context of Coleman's Euclidean wormholes that arise when axion fields reside in the effective field theory. In my talk I will briefly overview this research area, explain what happened in the last years, with some focus how modern developments like holography and string theory could help in our understanding. I then sketch some recent work of mine that suggests that these wormholes do not contribute in the path integral whenever they are macroscopic (and hence semi-classical).