Vienna-Theory-Lunch-Club--Seminar SS09

by Daniel Grumiller & Beatrix Hiesmayr & Maximilian Attems & Marcus Huber

Di 12:30-13:30

abwechselnd auf der

TU Wien (E136, 10. Stock (gelb))

oder der

Uni Wien (Boltzmanngasse 5, 5.Stock, gr. Seminarraum (Schrödinger Hs )

 Idee/Idea: Wie auf vielen Elite Unis praktiziert, wollen wir ein Lunch-Seminar etablieren, das aktuelle Themen der Theoretischen Physik, die auf unseren Unis von DiplomandInnen, DoktorandInnen und Postdocs behandelt werden, aufgreifen. Das Niveau soll so sein, dass jeder Student und jede Studentin am Ende des Studiums dem Vortrag folgen kann! Die Vortragenden werden auch ermutigt, keinen "perfekten" Vortrag zu halten, sondern haupsächlich zu motivieren, warum sie dieses Thema gewählt haben, und dabei dürfen auch durchaus offene Fragen und Probleme behandelt werden. Damit es zu praktisch keinen "Zeitverlust" kommt, wird gratis ein Mittagessen (Pizza,...) zur Verfügung gestellt. We want to establish a Graduate Student Lunch Club as praticed at other institutions like MIT. The seminars are designed for graduate students and should be accesible to all students. Students before their Diploma are particularly encouraged to attend so that they may learn about research begin performed on both universities. Speakers are encouraged to focus also on their motivation why they chose this particular topic and raise open questions. In order to avoid any "loss of time" we provide a free lunch (pizza,...). Wie kann ich teilnehmen?/ How can I join? Einfach erscheinen! Falls man per Email informiert werden möchte, besuche die Seite Mailinglist oder Mail an Beatrix.Hiesmayr et univie.ac.at oder an grumil et hep.itp.tuwien.ac.at Just attend! To receive infos per email got to Mailinglist or drop an email to Beatrix.Hiesmayr et univie.ac.at or grumil et hep.itp.tuwien.ac.at

 10. März 2009 TU Wien David Burke (VUT) Confined Monopoles (pdf) A basic introduction to magnetic monopoles will be presented. Magnetic monopoles in non-Abelian gauge theories broken to a non-Abelian subgroup have enjoyed renewed interest with a new emphasis on electromagnetic duality and the dual superconductor model for confinement. In order to study such objects at the quantum level supersymmetric models have been invaluable in trying to ascertain the key features which we may expect in a non-supersymmetric model while still having better control over the model. Here we will try to build up to describing such an N=2 SUSY model and discuss some of its intriguing aspects. 17. März 2009 Uni Wien Antti Gynther (VUT) QCD at high temperatures: what have we learned about quark-gluon plasma (pdf) During the last few years, heavy-ion collisions have taught us a great deal about the properties of quark-gluon plasma, some of which have proven to be quite surprising. Discovery that the produced matter behaves as a nearly perfect liquid has prompted a big theoretical challenge and has even brought some of the research in string theory back to its roots. In this lunch talk I will give an introductory review on some of the things we have learned about quark-gluon plasmas and the theoretical challenges it has provided us with. 24. März 2009 TU Wien Roman Höllwieser (VUT) Center Vortices in Lattice QCD (pdf) A basic introduction to Lattice QCD and the center vortex model of quark confinement will be presented. Quantum Chromodynamics (QCD) is a theory of the strong interaction, a fundamental force describing the interactions of the quarks and gluons making up hadrons (such as the proton, neutron or pion). Lattice QCD (LQCD) is the study of the SU(3) Yang–Mills theory of color-charged fermions (the quarks), in terms of quantum field theory on a four dimensional space-time lattice. It is the main tool for probing QCD in the non-perturbative regime, where QCD predicts quark confinement, which means that the force between quarks does not diminish as they are separated. The center vortex model has been proposed as an explanation of confinement in non-Abelian gauge theories. Center vortices, quantized magnetic flux-lines, compress the gluonic flux into tubes and cause a linearly rising potential at large separations. Here, this model will be formulated in SU(2) lattice gauge theory. 31. März 2009 Uni Wien Bertalan Juhasz (SMI) Antimatter does matter (pdf) Every particle in Nature has an antimatter counterpart, a kind of "mirror" particle. According to the fundamental Charge-Parity-Time (CPT) symmetry, which seems to be valid in all physical processes, a particle and its antiparticle should have identical properties like mass, charge, etc. (apart from a negative sign here and there). Moreover, our current understanding of particle physics suggests that matter and antimatter should always be created in equal amounts - either in laboratories now or during the Big Bang back then. However, our Universe seems to be made of matter only; there are no antigalaxies with antistars and antiplanets. One possible explanation to this apparent asymmetry is CPT violation, which would result in a non-equality of the properties of a particle and its antiparticle. The goal of the ASACUSA collaboration at CERN (Geneva, Switzerland) is to study the properties of antiproton, the antimatter counterpart of proton, and thus search for a violation of CPT symmetry. The first part of the talk will focus on measurements on a unique exotic molecule, the antiprotonic helium, which consists of a helium nucleus, an antiproton, and an electron. The unusually long lifetime of this molecule enables us to measure some of its transition frequencies using laser spectroscopy, and extract values for the charge and mass of the antiproton. The second part of the talk will explain a planned experiment to measure the ground-state hyperfine splitting of antihydrogen using an atomic beamline and microwave spectroscopy. According to some theoretical models, the hyperfine splitting is particularly sensitive to CPT violating effects. 17. April 2009 ESI Roman Jackiv (MIT) 4 -> 3 dimensional reduction of the Weyl tensor and Einstein-Weyl Theory Kaluza-Klein reduction of conformally flat spaces is considered for arbitrary dimensions. The corresponding equations are particularly elegant for the reduction from four to three dimensions. 21. April 2009 TU Wien Olaf Hohm (Groningen University) Massive gravity (pdf) In this talk I introduce a recent proposal for a theory of massive gravity in three dimensions. First, I review the consistency problems for massive spin-2 theories in generic dimensions. Then, I explain special features in three dimensions such as the possibility of gauge invariant mass terms and, in particular, topologically massive gravity. Using these special three-dimensional features I explain how a non-linear "covariantisation" of massive gravity can be introduced in D=4 via higher-derivative couplings. 28. April 2009 TU Wien Iva Brezinova (VUT) Anderson Localization of a Bose-Einstein Condensate (pdf) In solid state physics, Anderson localization describes a metal-insulator transition due to disorder in the crystal lattice. The conductance through such a disordered lattice vanishes although classically, one would expect diffusion. Within Feynman's picture of quantum mechanics, Anderson localization can be attributed to the interference of multiply scattered paths. This purely quantum mechanical effect leads to a transition from extended to localized electron waves within the crystal. Although the concept of Anderson localization is by now 50 years old, there are still open questions. Especially the interplay between Anderson localization and interactions between the particles is not yet well understood. Recently, the first direct experimental observation of Anderson localization of matter waves has been achieved in a Bose-Einstein condensate [1]. Anderson localization of a Bose-Einstein condensate opens new ways to investigate the effect of interactions on Anderson localization. In this talk, a review on Anderson localization and Bose-Einstein condensation will be given. It will be explained how an interacting localized Bose-Einstein condensate can be achieved. Finally, the newest theoretical results on Anderson localization of an interacting Bose-Einstein condensate will be presented. [1] J. Billy et al. Nature 453, 891 (2008) 5. Mai 2009 Uni Wien Catalina Petrascu (Frascati, Italien) Is it always that electrons are unfriendly? (pdf) We believe that all processes in Nature are based on the  fundamental principle relating spin and symmetry, sometimes known as the Pauli Exclusion Principle (PEP). Star evolution, chemical processes, atoms, protons and neutrons are just few examples of  PEP at work. WE are examples of PEP at work!It is a well known fact that electrons are “selfish”, they do not like to share the same quantum state; i.e. in any object where electrons are present, let’s take an atom, each one has a unique set of quantum numbers – no other electron share it! Such a matter of fact is not a miracle – it has its deep roots in the concept of identical particles, which, together with the more elusive concept of spin, generates in the quantum mechanics the so-called spin-statistics relation, assigning always to the fermions (particles with half integer spin, as electrons) an antisymmetric wave-function (obeying the PEP principle), while to the more friendly bosons (particles with integer spin, as the photons) a symmetric one -they can and sometime do share the same quantum state. Now, why to wonder about the PEP validity? Are we not happy it works? Otherwise we would not exist after all…. The quest for PEP validity was actually initiated by Pauli himself in 1945, when, in his Nobel lecture (prize received for the PEP discovery!) he said: “... Already in my original paper I stressed the circumstance that I was unable to give a logical reason for the exclusion principle or to deduce it from more general assumptions. I had always the feeling and I still have it today, that this is a deficiency. ... The impression that the shadow of some incompleteness [falls] here on the bright light of success of the new quantum mechanics seems to me unavoidable” Since then, in spite of more than 50 years of physics, we are still wondering about PEP validity, since we were not yet able to answer to Pauli – we did not yet find the logical reason beyond PEP! On the contrary, isolated voices are even claiming that sometimes it might not even hold…blasphemy? So, we are entitled and motivated to look for its violation, and such experiments are done following various, ingenious, methods. We shall present the origin of PEP and the VIP experiment, the most ambitious search for its violation by electrons, as well as a discussion about possible outcomes – Nobel or….IgNobel (big difference, isn’t it?). Because (citing O. Greenberg):“Hopefully either violation will be found experimentally or our theoretical efforts will lead to understanding of why only bose and fermi statistics occur in Nature”. 12. Mai 2009 TU Wien Michael Ortner (Uni Innsbruck) 1D Fermi gas - The Luttinger Liquid (pdf) One dimensional systems often behave quite differently from higher dimensional ones. In this talk i would like to present one of these peculiarities by treating a one dimensional Fermi gas in the low energy limit. With a standard textbook approach, the Bosonization, we can study the phases of such a system, called a Luttinger Liquid. After this elementary excursion i would like to give an outlook on how this theory is applied and used also in current projects. 19. Mai 2009 Uni Wien Martin Zdrahal (Uni Wien) What can the dispersive methods tell us about the $\pi\pi$ scattering? Pions are the simplest particles interacting by the strong interaction. The pion-pion scattering is therefore the simplest nontrivial hadron scattering process and thereby an important source of information about the strong interactions. In particular it is very sensitive to the mechanism of spontaneous chiral symmetry breaking. The most important characteristic of it is given by the scattering lengths. The chiral perturbation theory is a natural tool for describing this process and gives a prediction of the scattering lengths. The dispersive methods based on requirements on the analytic form of the amplitudes together with the validity of unitarity relations showed themselves to be useful in two ways: combined with the chiral perturbation theory they give a more accurate theoretical prediction for the scattering lengths; and using them alone as a model-independent way based only on the very general principles of the quantum field theories they give some general restrictions of the numerical values of the lengths and can also give methods how to obtain experimentally these values from different processes. We will concentrate mainly on the second aspect and show the method enabling us to get them from the appearance of the so-called cusp in $K \to 3\pi$ decay. 26. Mai 2009 TU Wien Jürgen Klepp (Uni Wien) Observation of mixed state phases with polarized neutrons (pdf) In a neutron polarimetry experiment the mixed state relative phases between spin eigenstates are determined from the maxima and minima of measured intensity oscillations. We consider evolutions leading to purely geometric, purely dynamical and combined phases. It is experimentally demonstrated that the sum of the individually determined geometric and dynamical phases is not equal to the associated total phase which is obtained from a single measurement, unless the system is in a pure state. 2. Juni 2009 Uni Wien Daniela Klammer (Uni Wien) Noncommutative Emergent Gravity (pdf) In search of a fundamental theory of quantum gravity, matrix models are a powerful tool. In this talk an introduction to matrix models of Yang-Mills type is given. It is shown how they lead to an emergent gravity theory, which does not require fine-tuning of a cosmological constant. Moreover the connection between gravity and noncommutative QFT is revealed. Cosmological solutions of Friedmann-Robertson-Walker type are discussed showing generically a big bounce, rather than a big bang. The mechanism is purely geometrical, no ad-hoc scalar fields are introduced. The solutions are stabilized through vacuum fluctuations and are thus compatible with predictions from quantum mechanics. This leads to a Milne-like universe after inflation, which appears to be in remarkably good agreement with observation. Thus the model may provide an alternative to standard cosmology possibly avoiding dark energy. 9. Juni 2009 TU Wien Marcus Huber (Uni Wien) What properties should an entanglement measure for multipartite quantum systems have? (pdf) Entanglement is a key feature in quantum information theory and a resource for many applications. However little is known about entanglement in higher dimensional systems, especially when many particles are involved. This talk will try to give a brief insight into the nature of entanglement, motivate the basic properties of entanglement measures and present two recent examples. 16. Juni 2009 Uni Wien Alexander Noll (TU Wien) Mirror Symmetry (pdf) Mirror symmetry is a duality between two string theories compactified on two different geometries. It has very interesting consequences: it allows one to compute correlation functions exactly, including instanton corrections, by relating them to certain computations which can be performed in the mirror theory. I will give a pedagocial introduction to the simplest case of mirror symmetry, namely T-duality for the closed bosonic string and explain the consequences. In particular, I will show that T-duality implies that there is a minimal length scale in string theory. I will then generalize the discussion to superstrings. 23. Juni 2009 TU Wien Christoph Spengler (Uni Wien) Quantum nonlocality and its phase space geometry The fact that quantum theory is irreconcilable with any local-realistic theory is one of the most seminal discoveries. This so-called quantum nonlocality can be ascribed to entanglement and manifests itself through the violation of a Bell inequality. Closer considerations within recent years have raised the question of whether there is a discrepancy between entanglement and nonlocality. This talk gives an introduction into this field of research and an overview on the latest state of knowledge. In order to get a deeper insight into the problem, the phase space geometry of entanglement and nonlocality will be compared. Here, the focus is on a set of states which is called the "magic simplex". 30. Juni 2009 Uni Wien Ana-Maria Piso (MIT) Solar Winds The solar wind is a stream of ionized particles, mainly hydrogen and helium, ejected by the Sun's corona. These particles achieve a very high kinetic energy and are thus able to escape the Sun's gravity. I will present here the solar wind model of Eugene Parker, in particular the velocity profile of the solar wind flux and the interplanetary magnetic field (IMF) that originates in the Sun and is carried into space by the solar wind. I will illustrate this model with the help of a Mathematica Demonstration Project.