Calendar of Physics Talks Vienna

On the scattering theory for the Dirac equation in the Schwarzschild-Anti-de Sitter space-time
Speaker:Guillaume Idelon-Riton (Grenoble)
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.
Date: Thu, 02.03.2017
Time: 14:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Raum 218, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel

Probing gravity with neutrons and antimatter
Speaker:Giovanni Manfredi (Institut de Physique et Chimie des Matériaux de Strasbourg)
Abstract:Recent years have witnessed a renewed spur of interest in the physics of antimatter. The motivation of this research is to compare the physical properties of matter and antimatter, for instance the spectral lines of antihydrogen or its behavior under the influence of gravity. The recently established collaboration GBAR (Gravitational Behavior of Antihydrogen at Rest), to which our Strasbourg group contributes, aims specifically at determining the gravitational acceleration of antihydrogen atoms by letting them fall in the gravitational field of the Earth [1]. In the first part of my talk, I will briefly illustrate the physical basis of the GBAR experiment and some related theoretical results obtained in our group [2]. On the other hand, experimental investigations on small objects (neutrons, ordinary atoms, Bose-Einstein condensates) evolving in the Earth’s gravitational field have been conducted for several years. In the early 2000s, the corresponding quantum gravitational states of ultracold neutrons were observed for the first time [3], followed by more recent investigations where several transitions between two such states were triggered by mechanical oscillations of the mirror plates that confine the neutrons [4]. Here, I will describe a technique to excite higher-energy states by applying a sinusoidal modulation with slowly varying frequency (chirp) to the confining mirror plates [5]. The method is based on the so-called autoresonance effect, whereby a classical nonlinear oscillator can be brought to arbitrary large amplitudes by driving it with a slowly chirped force. The proposed experiment should make it possible to observe the quantum-classical transition that occurs at high neutron energies. Furthermore, it provides a technique to realize superpositions of gravitational quantum states, to be used for precision tests of gravity at short distances. [1] P. Perez and Y. Sacquin, Class. Quantum Grav. 29, 184008 (2012) [2] G. Manfredi, P.-A. Hervieux, F. Haas, New J. Phys. 14, 075012 (2012); O. Morandi, P.-A. Hervieux, G. Manfredi, Phys. Rev. A 89, 033609 (2014). [3] V. V. Nesvizhevsky et al., Nature (London) 415, 297 (2002). [4] T. Jenke, P. Geltenbort, H. Lemmel, H. Abele, Nature Phys. 7, 468 (2011). [5] G. Manfredi, O. Morandi, L. Friedland, T. Jenke, H. Abele, Phys. Rev. D 95, 025016 (2017).
Date: Fri, 03.03.2017
Time: 15:30
Location:Atominstitut, Hörsaal, Stadionallee 2, Wien 2
Contact:H. Abele