In addition to the Vienna relativity seminars, the calendar above sometimes contains other events of interest to members of the relativity group. The seminars of the Vienna relativity group are listed below.
Unless explicitly stated otherwise, the regular (not-lunch) relativity seminars take place in Room 218 2nd floor, Währingerstrasse 17. The Mathematical Physics Seminars take place on Tuesdays at 14.15. The Particle Physics Seminars take place on Tuesdays at 16.15.
- Wednesday March 1, lunch seminar, 13:00, Wolfgang Wieland (Perimeter): New boundary variables for classical and quantum gravity
Abstract: In my talk, I will present a new representation of loop quantum gravity with spinors as the fundamental configuration variables. I will show, in particular, that the discrete loop quantum gravity spin degrees of freedom (on a spin-network) can be related to classical surface degrees of freedom of the gravitational field on a null surface. The approach is based on the covariant Hamiltonian formulation for a manifold with (inner) null boundaries. The underlying action consists of the the self-dual action in the bulk plus an additional boundary term. The boundary term is required, because otherwise the action is not functionally differentiable. On the null boundary, the most natural such boundary term can be written in terms of spinors. The resulting canonically conjugate variables on the null surface are a spinor and a spinor-valued two-surface density. The quantisation of both the constraints (reality conditions) and the boundary symplectic structure reproduces the loop quantum gravity Hilbert space in the spinorial representation. The talk is based on the papers [arXiv:1611.02784, arXiv:1604.07428, arXiv:1107.5002].
- Thursday March 2, 14:00, Guillaume Idelon-Riton (Grenoble): On the scattering theory for the Dirac equation in the Schwarzschild-Anti-de Sitter space-time
Abstract: I will first describe the Schwarzschild-Anti-de Sitter spacetime and the geometrical properties that makes it interesting to look at when studying hyperbolic equations. I will then present the Dirac equation in this spacetime and investigate quickly the Cauchy problem. The solution is then analyzed from the point of view of scattering theory. First, I will look at this solution in the asymptotic region of the spacetime and give a result about the asymptotic completeness and the asymptotic velocity. Then, I will look at local properties of these fields for large time and give a lower bound on the local energy decay using the construction of exponentially accurate quasimodes. I will then present some tools to obtain an upper bound will then be such as the resonances and the WKB solutions that should allow to localize these resonances.
- Thursday, March 9, 14:00, Tim Paetz (Vienna): TBA
- Thursday, March 23, 14:00, Andrzej Rostworowski (Cracow): Higher order perturbations of Anti-de Sitter space and time-periodic solutions of vacuum Einstein equations
Abstract: Motivated by the problem of stability of Anti-de Sitter (AdS) spacetime, I will discuss nonlinear gravitational perturbations of maximally symmetric solutions of vacuum Einstein equations in general and the case of AdS in particular. I will present the evidence that, similarly to the self-gravitating scalar field at spherical symmetry, the negative cosmological constant allows for the existence of globally regular, asymptotically AdS, time-periodic solutions of vacuum Einstein equations that bifurcate from linear eigenfrequencies of AdS. Interestingly, preliminary results indicate that the number of time-periodic solutions bifurcating from a given eigenfrequency equals the multiplicity of this eigenfrequency. The talk will be based on the recent preprint https://arxiv.org/abs/1701.07804
- Thursday March 30, 14:00, Sari Ghanem (Potsdam): The decay of SU(2) Yang-Mills fields on the Schwarzschild black hole with spherically symmetric small energy initial data
Abstract: First, I will present the Yang-Mills equations on arbitrary fixed curved space-times, valued in the Lie algebra associated to any arbitrary Lie group. Thereafter, I will expose recent results with Dietrich Häfner concerning the Yang-Mills fields valued in the Lie algebra su(2) associated to the Lie group SU(2), propagating on the Schwarzschild black hole. We assume that the initial data are spherically symmetric, satisfying a certain Ansatz and have small energy, which excludes the stationary solutions which do not decay. We then prove uniform decay estimates in the entire exterior region of the black hole, including the event horizon, for gauge invariant norms on the Yang-Mills curvature generated from such initial data, including the $ L^\infty $ norm of the so-called middle components. This is done by proving in this setting, a Morawetz type estimate that is stronger than the one assumed in previous work, without passing through the scalar wave equation on the Yang-Mills curvature, using the Yang-Mills equations directly.
- Thursday, April 6, 14:00, Juan Valiente-Kroon (Queen Mary): TBA
- Thursday, April 27, 14:00, Dennis Raetzel (Vienna): TBA
- Thursday, May 4, 14:00, joint relativity - mathematical physics seminar, Robert Seiringer (ISTA): The excitation spectrum in a Bose fluid
Abstract: Of particular relevance for an understanding of the low-temperature properties of a quantum system is the excitation spectrum. With the exception of exactly solvable models in one dimension, rigorous results on its structure are lacking and one has to resort to adhoc approximations to make predictions. We present recent progress on this question for bosonic many-body quantum systems with weak two-body interactions. Such systems are currently of great interest, due to their experimental realization in ultra-cold atomic gases. We investigate the accuracy of the Bogoliubov approximations, which predicts that the low-energy spectrum is made up of sums of elementary excitations, with linear dispersion law at low momentum. The latter property is crucial for the superfluid behavior of the system.
- Thursday, May 11, 14:00, Katharina Radermacher (Stockholm): TBA
- Thursday, May 18, 14:00, Stefan Hollands (Leipzig): TBA
- Thursday, TBA, 14:00, Michael Eichmair (Vienna): TBA
Location (unless indicated otherwise): Währinger Str. 17
- Room 218 on the 2nd floor for standard seminars, and
- Common room, first floor, for lunch seminars.