PIRSA:23100076

Metric signature transitions and the cosmological constant

Gielen, S. (2023). Metric signature transitions and the cosmological constant. Perimeter Institute. https://pirsa.org/23100076

Gielen, Steffen. Metric signature transitions and the cosmological constant. Perimeter Institute, Oct. 05, 2023, https://pirsa.org/23100076 

          @misc{ pirsa_PIRSA:23100076,
            doi = {10.48660/23100076},
            url = {https://pirsa.org/23100076},
            author = {Gielen, Steffen},
            keywords = {Quantum Gravity},
            language = {en},
            title = {Metric signature transitions and the cosmological constant},
            publisher = {Perimeter Institute},
            year = {2023},
            month = {oct},
            note = {PIRSA:23100076 see, \url{https://pirsa.org}}
          }

Steffen Gielen

University of Sheffield

Talk number
PIRSA:23100076
Collection
Talk Type
Subject
Abstract

In classical relativity we usually think of the metric signature as fixed, but quantum cosmology already forces us to consider more general situations such as transitions from Riemannian to Lorentzian signature. I will discuss the less studied phenomenon of an overall "flip" where all metric components change sign simultaneously (e.g., from "East Coast" to "West Coast" signature). Such an overall flip can represent saddle point solutions in quantum cosmology, or appear classically in the Plebański formalism or even a slight extension of Einstein--Hilbert gravity. Interestingly, at such a transition the cosmological constant can change both sign and magnitude, with a pure sign change being the most minimalistic proposal. Cosmological solutions transitioning classically between de Sitter and anti de Sitter can be found immediately, and the quantisation of a minisuperspace model turns out to be simpler than in the fixed signature case: in particular, the gravitational action reduces to a pure boundary term. Various other applications and the relation to unimodular gravity are also discussed.

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Zoom link: https://pitp.zoom.us/j/93255772501?pwd=bWhzZUVBOTM2a3QvTGlXVGJ5TlZnUT09