Vienna Theory Lunch Club Seminar

by David Burke, Niklas Johansson, Theodor Adaktylos, Andreas Gabriel and Christoph Spengler

Tuesdays 12:15-13:30

held alternatively at:

TU Wien ( Wiedner Hauptstr. 8-10, yellow area, 10th floor, seminar room E136 )

Uni Wien ( Boltzmanngasse 5, 5th floor, Schrödinger HS / large seminar room )

We thank our kind sponsors:

Dean of physics, TU

Dean of Physics, Uni Wien

Idee: Idea:	Wie auf vielen Universitäten praktiziert wollen wir ein Lunch-Seminar etablieren, das aktuelle Themen der Theoretischen Physik, die von DiplomandInnen, DoktorandInnen und PostDocs behandelt werden, aufgreift. Das Niveau soll so gewählt werden, dass jeder Student und jede Studentin am Ende des Studiums dem Vortrag folgen kann. Die Vortragenden werden ermutigt keinen "perfekten" Vortrag zu halten, und sollen hauptsächlich Ihre Motivation, warum sie dieses Thema gewählt haben, wiedergeben. Dabei dürfen durchaus offene Fragen und Probleme behandelt werden. Damit es zu keinem "Zeitverlust" kommt, wird Mittagessen (Pizza, Sushi) gratis zur Verfügung gestellt.	We want to establish a lunch seminar as practiced at other universities. The focus is on recent theoretical research done by Master students, PhDs and PostDocs. The seminar is designed for graduate students but should also be comprehensible to advanced undergraduate students. Pre-diploma students are particularly encouraged to attend so that they receive an overview of research activities conducted at both universities. Speakers are also encouraged to focus on their motivation for choosing their particular topic and to present open questions. In order to avoid any "loss of time" we provide a free lunch (pizza, sushi).
Wie kann ich teilnehmen? How can I join?	Einfach erscheinen! Um per Email informiert zu werden, bitte in die Mailinglist eintragen oder Mail an dburke at hep.itp.tuwien.ac.at oder an christoph.spengler at univie.ac.at	Just attend! To receive informations via email go to the Mailinglist or drop an email to dburke at hep.itp.tuwien.ac.at or christoph.spengler at univie.ac.at

02. März 2010 TU Wien	Magdalena Larfors (LMU Munich)	On the stability of string vacua (pdf) Compactifications of string theory constitute a promising framework for reproducing interesting cosmological features, such as inflation. An important subtlety in these constructions is the stabilization of moduli; four-dimensional scalar fields that describe fluctuations of the geometry of the compactified dimensions. In this talk, I will review how moduli can be fixed in compactifications of type II string theory. I will also discuss cosmological features of the resulting four-dimensional vacua, and how metastable vacua can decay through the formation of new vacuum bubbles.
09. März 2010 Uni Wien	Mario Ziman (RCQI Bratislava)	Quantum measurements and estimations (pdf) In this seminar we will investigate inverse problems of quantum physics. That is, the ones associated with an identification of quantum properties out of observed measurement statistics. The goal is to understand what is measured in quantum measurements and introduce the concept of quantum observables as the most general description of quantum measurements. We will formulate the problem of estimation of the wave function (Pauli problem) and density operators. Analyzing a simplified model of Stern-Gerlach experiments we will come to the concept of positive operator valued measure (POVM) as the mathematical representation of quantum observables. We will give a formal definition and provide basic mathematical properties concerning POVMs (Gleason's theorem, Naimark theorem, etc). We will introduce the concept of informationally complete measurements enabling us to experimentally observe and reconstruct quantum states. If some time remains (I doubt) we will discuss under which circumstances some nontrivial information can be acquired from individual experimental clicks. In particular, we will analyze the existence of minimum-error conclusions and unambiguous conclusions for the problem of single-shot discrimination among a pair of pure quantum states.
16. März 2010 TU Wien	Johanna Knapp (TU Wien)	D-Branes, Topological Strings and Mirror Symmetry (pdf)
23. März 2010 Uni Wien	Jan Bouda (Uni Brno)	Privacy amplification, message authentication and randomness extractors
13. April 2010 TU Wien	Tomas Tyc (Uni Brno)	Invisibility Devices Electromagnetic cloaking is a modern and rapidly developing area of optics. Its objective is to encapsulate an object into a carefully designed material with special optical properties, such that the light rays flow smoothly around the object and after passing it, restore their original direction. This creates the illusion that the space is empty. Several invisibility cloaks will be discussed in the talk with the focus on a non-Euclidean cloak that might turn invisibility into a practical technology.
20. April 2010 Uni Wien	Adam Ruzicka (Uni Wien)	Interacting galaxies - numerical simulations in astrophysics Galaxies are considered the building blocks of the Universe. They are gravitationally bound systems of stars and gas. However, their kinematics cannot be explained within the framework of the classical Newtonian/Einstein theories of gravity unless additional mass is introduced. The visible matter corresponds to 10% of the mass needed to explain the formation and evolution of galaxies. To resolve the difficulty, the standard cosmology introduces the mysterious invisible dark matter. This matter does not interact in any way but gravitationally. The visible galactic matter resides in the centers of extended dark matter structures - galactic halos. Already few hundred milion years after the Big Bang the clustering of the dark matter gave rise to the first dark matter halos. Theis mass was increasing due to the hierarchical merging of smaller structures. Later, the visible (baryonic) matter cooled down and seetled down in the centers of the dark matter halos. The first galaxies appeared. The structure of the Universe seems hierarchical on all scales, and galaxies have formed a large variety of groups as well. Apparently, galaxies must interact, and their encounters or even mergers influence critically their evolution. Numerical simulations and the computational astrophysics are nowadays the most powerful tools to learn what is behind the remarkable variety of galaxies. However, once observational data are available for a galactic system, they put a number of constraints on every theoretical model of such a system regarding the choice for the right combination of the initial conditions in order to reproduce the observations. Astrophysicists are forced to deal with extended sets of model parameters and initial conditions. We have shown that such high-dimensional parameter spaces may be searched through on a reasonable time-scale if a simplified astrophysical model of the galactic interaction is employed in a combination with an automated evolutionary code looking for the optimal solution to a problem. I will present our approach to modeling galactic interactions based on the use of genetic algorithms.
27. April 2010 TU Wien	Luzi Bergamin (Aalto University)	Transformation optics and the geometric interpretation of linear media Abstract: In the field of Metamaterials (artificial media in electromagnetics) the geometric design of effective medium parameters has become very popular recently. As basic idea of this design tool called "transformation optics" the trajectories of light are engineered directly by means of coordinate transformations (diffeomorphisms), the necessary effective media parameters then follow in an algebraic way from these transformations. This can be used to design various devices such as invisibility devices (see the talk by Tomas Tyc), beam shifters or benders etc. In my presentation I will review the foundations of transformation optics and compare it to other geometric interpretations of media, in particular the Fresnel equation in the geometric optics limit. This will include in particular: derivation of electrodynamics of linear media using the pre-metric approach by Hehl and Obukhov; invariance of electrodynamics and the idea of transformation optics; extended Fresnel equation and geometric optics limit; birefringence and bi-metricity of generic linear media; outlook to future research topics.
04. Mai 2010 Uni Wien	Karl-Georg Schlesinger (Uni Wien)	Geometric Langlands duality and physics We review the approach to the geometric Langlands program for algebraic curves via S-duality of an N=4 supersymmetric four dimensional gauge theory, initiated by Kapustin and Witten in 2006. We sketch some of the central further developments. Placing this four dimensional gauge theory into a six dimensional framework, as advocated by Witten, holds the promise to lead to a formulation which makes geometric Langlands duality a manifest symmetry (like coavariance in differential geometry). Furthermore, it leads to an approach toward geometric Langlands duality for algebraic surfaces, reproducing and extending the recent results of Braverman and Finkelberg.
11. Mai 2010 TU Wien	Michael Wohlgenannt (TU Wien)	Pointless Geometry We will discuss some basic notions of noncommutative geometry and a few properties of noncommutative quantum field theories, most prominently the so-called UV/IR mixing. Also relations to other fields will be of interest.
18. Mai 2010 Uni Wien	Fabio Costa (Uni Wien)	Classical Entropy in Coarse Grained Quantum Fields A characteristic feature of (free) quantum fields is that, when the field is in the vacuum or in a low energy state, the Von Neumann entropy associated with a region of space is proportional to the area of the region, rather than to the volume as is typical for classical systems. We study the effect of introducing an error in the measurement of the field observables, formalized as a coarse grain in phase space, for the case of a free Klein Gordon field. We show that for sufficiently large coarse grain parameters the state of the field becomes separable and its Wigner function positive. For large errors it can be properly interpreted as a classical probability distribution, as the Von Neumann entropy reduces to the classical Shannon entropy. A volume scaling of the entropy associated to a region of space is then proved. These results give an indication of how classical fields can emerge from quantum fields under the assumption of coarse grained measurements.
01. Juni 2010 TU Wien	Wolfgang Wieland (TU Wien)	Elements of Loop Quantum Gravity Loop Quantum gravity (LQG) is an attempt to construct a canonical quantisation of the gravitational field. Starting with an elementary --i.e. understandable-- introduction to the theory I will first discuss the construction of the underlying Hilbert space of LQG together with the major predictions on the so-called kinematical level. These include the fundamental discreteness of geometry at the Planck-scale, represented by the discrete spectrum of geometric operators corresponding to classical length, area and volume. After this introduction I will present recent developments of our group concerning the quantisation of the so-called Hamiltonian constraint, implementing the dynamics of the theory.
08. Juni 2010 Uni Wien	Branislav Cvetković (Institute of Physics Belgrade)	Conserved charges in 3D gravity Abstract: The covariant canonical expression for the conserved charges, proposed by Nester, is tested on several solutions in 3D gravity with or without torsion and topologically massive gravity. In each of these cases, the calculated values of energy-momentum and angular momentum are found to satisfy the first law of black hole thermodynamics.
15. Juni 2010 TU Wien	Christoph Mayrhofer (TU Wien)	GUT Models from F-Theory
22. Juni 2010 Uni Wien	Katrien Kolenberg (Uni Wien)	Amplitude and phase modulation in pulsating stars A large fraction of the stars in the Universe displays instabilities in the form of pulsations on time scales between minutes and thousands of years. These oscillations are mostly revealed by brightness changes, and prove to be very useful diagnostics for our understanding of stellar structure and evolution. My own research focuses on the mysterious phenomenon of amplitude and phase modulation in the class of pulsating RR Lyrae stars. I will present an overview of these objects, their use in astronomy, the observational facts so far - including some exciting results obtained very recently, and the proposed hypotheses for explaning the phenomenon. As this is one of the most stubborn and longstanding problems in stellar astrophysics, I look forward to a cross-disciplinary exchange on the topic of oscillations and instabilities.
29. Juni 2010 TU Wien	Stefanie Gräfe (TU Wien)	Attosecond electron dynamics in strong laser fields In this talk, the physics of atoms and molecules in strong laser fields is introduced. An overview about different phenomena occuring in strong laser fields, such as strong-field ionization of the atom or molecule and subsequent rescattering of an liberated electron on the ionic core are presented. Taking a recent experiment as an example, I will show how an intense infrared laser field with a duration of only a few optical cycles allows one to actively control and steer the electronic dynamics in molecules. Further, methods how to measure the success of such a control experiment will be presented.

Program Winter Semester 2009/2010
Program Summer Semester 2009