|
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 |
|