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Calendar of Physics Talks Vienna
| Speaker: | Edgar Shaghoulian (Cornell) |
| Abstract: | I will review the role of replica wormholes in deriving a unitary Page curve for Hawking radiation and discuss extensions to flat spacetime and cosmology. I will also discuss general consistency conditions that guide the search for such nontrivial saddles in the gravitational path integral. |
| Date: | Tue, 06.10.2020 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | https://moodle.univie.ac.at/mod/bigbluebuttonbn/guestlink.php?gid=x8o6ILSKJuC9 |
| Contact: | Céline Zwikel |
| A Bakry-Emery Almost Splitting Result With Applications to the Topology of Black Holes and Cosmology |
| Speaker: | Markus Khuri (Stony Brook) |
| Abstract: | The almost splitting theorem of Cheeger-Colding is generalized to the setting of almost nonnegative m-Bakry-Emery Ricci curvature, in which m is positive and the associated vector field is not necessarily required to be the gradient of a function.In this context it is shown that with a diameter upper bound and volume lower bound the fundamental group of such manifolds is almost abelian.Furthermore, extensions of well-known results concerning Ricci curvature lower bounds are given for generalized m-Bakry-Emery Ricci curvature.This analysis is then applied to stationary vacuum black holes in higher dimensions to find that low temperature horizons must have limited topology,similar to the restrictions exhibited by (extreme) horizons of zero temperature. Lastly, applications to cosmology are also described.Here restrictions are obtained on the list of possible topologies of the universe. |
| Date: | Thu, 08.10.2020 |
| Time: | 16:00 |
| Duration: | 90 min |
| Location: | https://zoom.us/j/4200372900?pwd=c01vb0FNRU94V0JVdWlnaDE0eUwwQT09 |
| Contact: | Piotr Chrusciel, David Fajman |
| The effective action of superrotation modes |
| Speaker: | Kévin Nguyen (King's College) |
| Abstract: | Starting from an analysis of four-dimensional asymptotically flat gravity in first order formulation, we show that superrotation reparametrization modes are governed by an Alekseev--Shatashvili action on the celestial sphere. This two-dimensional conformal theory describes spontaneous symmetry breaking of Virasoro superrotations together with the explicit symmetry breaking of more general Diff(S2) superrotations. We arrive at this result by first reformulating the asymptotic field equations and symmetries of the radiative vacuum sector in terms of a Chern--Simons theory at null infinity, and subsequently performing a Hamiltonian reduction of this theory onto the celestial sphere. |
| Date: | Thu, 08.10.2020 |
| Time: | 16:00 |
| Duration: | 60 min |
| Location: | https://tuwien.zoom.us/j/95482849369?pwd=SkU2WU5hMVJBQWsyVlFXRlRvQlIvdz09 |
| Contact: | Laura Donnay |
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