Torsdag 23. oktober kl. 14.15 i rom C-101, Kjølv Egelands hus. :
Professor Alan Coley, Dalhousie Universitet, Halifax, Nova Scotia, Canada, holder foredrag:
Averaging in spherically symmetric comsmology
We discuss the averaging problem in general relativity using theform of the macroscopic gravity equations in the case of sphericalsymmetry in volume preserving coordinates. In particular, we calculate the form of the correlation tensor under some reasonable
assumptions on the form for the inhomogeneous gravitational field and matter distribution.
On cosmological scales, the correlation tensor in a Friedmann-Lemaitre-Robertson-Walker background is found to be of the form of a spatial curvature.
On astrophysical scales the correlation tensor can be interpreted asthe sum of a spatial curvature and an anisotropic fluid. We briefly discuss the physical implications of these results.
Fredag 24.oktober kl. 12.30. Merk tiden.
Sted: Rom E-541, lunsjrommet i femte etasje, Kjølv Egelands hus.
Gjesteforsker, Post. Doc. Nicos Pelayas Dalhousie Universitet, Halifax, Nova Scotia, Canada, holder foredrag
Geometric properties of the Kundt class..
A four dimensional Lorentzian geometry that admits a null congruence withcertain kinematic features defines the Kundt class of metrics. These spacetimes play a key role when a characterization of geometries based on scalar polynomial curvature invariants is performed. I shall discuss the connection between the kinematic and the curvature properties of these spacetimes.
I will then focus on a particular subclass of the Kundt metrics and show how the Riemann tensor and all of its derivatives become algebraically special and also give a partial algebraic classification for the first covariant derivative of the Riemann tensor.