# Calendar of Physics Talks Vienna

 Vienna Theory Lunch Club - What can the dispersive methods tell us about the $\pi\pi$ scattering?
 Speaker: Martin Zdrahal (Uni Wien) Abstract: 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. Overview Lunch Club Date: Tue, 19.05.2009 Time: 12:30 Duration: 60 min Location: University of Vienna, Boltzmanngasse 5, 5th Floor, Large Seminar Room Contact: Max Attems, Daniel Grumiller, Beatrix Hiesmayr

 Structures and Phase Transitions of Metal on Ge(111) by LEEM and STM
 Speaker: Prof. Shirley Chiang (Department of Physics, University of California/USA) Abstract: We have recently used both low energy electron microscopy (LEEM) and scanning tunneling microscopy (STM) to study the structures and surface phase transitions for Pb, Ag, and Au adsorbed on Ge(111). Our LEEM results show that the (√3x√3)R30°-β <-> (1x1) phase transition on Pb/Ge(111), even though it is first-order, is characterized by the thermal fluctuations of well-defined domains throughout the coexistence region (170-190°C). We have used LEEM to follow the phase transformation in real time and to explore the phase diagram of the system. For Ag on Ge(111), STM data show regions with several different known structures, the (4x4) with 0.375 ML coverage, the (√3x√3)R30° structure with 1ML coverage, and small regions of (3x1) structure. LEEM videos show that the (4x4) phase grows with a high dependency on surface steps and faceting of the surface as the phase grows from the steps. Although LEEM images show a disordered phase with no contrast near the desorption temperature, both the (4x4) and (√3x√3)R30° phases recondense on the surface when it is cooled. For Au on Ge(111), both STM and LEEM data show the expected Stranski-Krastanov growth mode with small islands of Au nucleating near step edges at low coverage. LEEM data also show hopping of 3D sub-micron sized islands at 400°C and phase fluctuations at the boundaries of regions of different structures of Au on Ge(111) at 620°C. Date: Tue, 19.05.2009 Time: 16:00 Location: Technische Universität Wien, Institut für Allgemeine Physik, Seminarraum 134A, Turm B (gelbe Leitfarbe), 5.OG, 1040 Wien, Wiedner Hauptstrasse 8-10 Contact: Prof. Dr. Peter Varga

 Recent progress in hadronic tau decays
 Speaker: Matthias Jamin (Univ. Autonoma de Barcelona) (Fakultät für Physik) Abstract: im Rahmen des Teilchenphysikseminars Date: Tue, 19.05.2009 Time: 16:15 Duration: 60 min Location: Erwin Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock Contact: H. Neufeld

 Neutron Interferometry and Berry Phase
 Speaker: Dr. Katharina Durstberger-Rennhofer (Atominstitut Wien) (Fakultät für Physik) Abstract: Seminar Date: Wed, 20.05.2009 Time: 16:15 Duration: 60 min Location: Kleiner Seminarraum, Boltzmanngasse 5, 5. Stock Contact: Reinhold A. Bertlmann