Vienna Theory Lunch Seminar

by Frederic Brünner, Sebastian Frank, Philipp Köhler, Albert Georg Passegger and Stephan Stetina

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 Lecture Hall / large seminar room )


We thank our kind sponsors:





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 stetina at oder an philipp.martin.koehler at

Just attend! To receive informations via email go to the Mailinglist or drop an email to stetina at or philipp.martin.koehler at


Mar 5 2013

TU Wien

S. Kumar Mallavarapu
(Washington University in Saint Louis)

Superfluid and semisuperfluid strings

Abstract: Recent literature mentions the formation of semisuperfluid strings in dense quark matter. The goal of the talk is to introduce these objects.  The talk shall begin with a mention of fundamental ideas about strings. Relevant geometrical and topological ideas about gauge fields will also be discussed

Mar 12 2013

Uni Wien

Bruno Mintz
(Rio State University)

Phase diagram and surface tension in the three-flavor Polyakov-quark-meson model

Abstract: We obtain the in-medium effective potential of the three-flavor Polyakov-Quark-Meson model as a real function of real variables in the Polyakov loop variable, to allow for the study of all possible minima of the model. At finite quark chemical potential, the real and imaginary parts of the effective potential, in terms of the Polyakov loop variables, are made apparent, showing explicitly the fermion sign problem of the theory. The phase diagram and other equilibrium observables, obtained from the real part of the effective potential, are calculated in the mean-field approximation. The obtained results are compared to those found with the so-called saddle-point approach. Our procedure also allows the calculation of the surface tension between the chirally broken and confined phase, and the chirally restored and deconfined phase. The values of surface tension we find for low temperatures are very close to the ones recently found for two-flavor chiral models. Some consequences of our results for the early Universe, for heavy-ion collisions, and for proto-neutron stars are briefly discussed.

Mar 19 2013

TU Wien

no lunch seminar

no lunch seminar

Apr 9 2013

Uni Wien

Jürgen Klepp
(Uni Wien)

Geometric Phase Properties in Neutron Optics Experiments

Abstract: Special properties of mixed-input phases are investigated experimentally with polarized neutrons. In the first part, I will explain a measurement of spinor phases for mixed input-states undergoing unitary evolutions. Phases of purely dynamical and purely geometric origin are measured as a function of the input purity of the neutron spin-state. Measuring suitable combinations of both, it has been demonstrated that the mixed-state geometric phase is not additive as it is the case for pure states. Nonadditivity is a natural consequence of the definition of the mixed-state phase as weighted average of the phase factors of all pure state components in the density matrix. In the second part, a test of the phase stability under noisy evolution is described.

Apr 16 2013

TU Wien

Christoph Saulder
(Uni Wien)


Abstract: One of the biggest mysteries in cosmology is Dark Energy, which is required to explain the accelerated expansion of the universe within the standard model. But maybe one can explain the observations without introducing new physics, by simply taking one step back and re-examining one of the basic concepts of cosmology, homogeneity. In standard cosmology, it is assumed that the universe is homogeneous, but this is not true at small scales (<200 Mpc). Since general relativity, which is the basis of modern cosmology, is a non-linear theory, one can expect some backreactions in the case of an inhomogeneous matter distribution. Estimates of the magnitude of these backreactions (feedback) range from insignificant to being perfectly able to explain the accelerated expansion of the universe. In the end, the only way to be sure is to test predictions of inhomogeneous cosmological theories, such as timescape cosmology, against observational data. If these theories provide a valid description of the universe, one expects aside other effects, that there is a dependence of the Hubble parameter on the line of sight matter distribution. The redshift of a galaxy, which is located at a certain distance, is expected to be smaller if the environment in the line of sight is mainly high density (clusters), rather than mainly low density environment (voids). Here we present a test for this prediction using redshifts and fundamental plane distances of elliptical galaxies obtained from SDSS DR8 data. In order to get solid statistics, which can handle the uncertainties in the distance estimate and the natural scatter due to peculiar motions, one has to systematically study a very large number of galaxies. Therefore, the SDSS forms a perfect basis for testing timescape cosmology and similar theories. The preliminary results of this cosmological test and the necessary calibrations will be discussed in this talk.

Apr 23 2013

Uni Wien

Mauricio Leston
(University of Buenos Aires)

Recents developments in non-perturbative QFT in curved spacetimes

Abstract: The so-called constructive QFT approach has provided several examples of interacting QFT for D=2 and D=3 Minkowski spacetime. That was done by the use of a well defined Euclidean functional integral. Some years ago, certain steps of this approach have been extended to D=2 static spacetimes. In this talk I will briefly review the Euclidean formulation of QFT in Minkowski space time, with special emphasis on the notion of reflection positivity and its importance in the constructive quantum field theory approach. Then, I will describe its recent extension to static spacetimes and some open problems. 

Apr 30 2013

TU Wien

No lunch seminar

No lunch seminar due to ESI anniversary symposium

For informations, visit

May 7 2013

Uni Wien

Maximilian Attems

Kinetic models of ultrarelativistic heavy ion collisions

Abstract: Ultrarelativistic heavy ion collision experiments probe strongly interacting matter under extreme conditions. The theory of the strong interaction quantum chromodynamics (QCD) predicts the creation of a Quark-Gluon Plasma (QGP) in such collisions. The theoretical description of the QGP dynamical evolution requires a wide range of tools. The initial condition of the nuclei before the collision as well as the gluon dynamics right after the collision is governed by Yang-Mills dynamics. Soon after the collision the system reaches local equilibrium and hydrodynamics describes the expansion. As the system gets more dilute, hadronic kinetic theory models become applicable. Progress on studies of the non-Abelian plasma instabilities for early stage dynamics and first results from a new pion gas implementation will be presented.

May 14 2013

TU Wien

Gergely Endrödi
(Universität Regensburg)

QCD thermodynamics in external magnetic fields

Abstract: The hadron resonance gas model and numerical lattice simulations are employed to study the response of the QCD vacuum to external magnetic fields, both at zero temperature and in the deconfinement/chiral transition region. The quark condensate and the trace anomaly are found to undergo magnetic catalysis at low temperatures and inverse catalysis around Tc, respectively. The magnetization is determined to be positive, indicating a paramagnetic QCD vacuum.

May 28 2013

Uni Wien

Gernot Eichmann
(Uni Graz)

Hadron physics in the Dyson-Schwinger approach

Abstract: I will give a brief overview of Dyson-Schwinger, Bethe-Salpeter and Faddeev equations and their application to hadron physics. Recent progress on various nucleon and delta elastic and transition form factors, nucleon Compton scattering, and a tetraquark interpretation of the sigma meson will be discussed.

Jun 4 2013

TU Wien

Hiromishi Nishimura
(Universitaet Bielefeld)

Confining gauge theories on R3 X S1 with Higgs

Abstract: I will review some aspects of confining gauge theories on R3 X S1. Yang-Mills theory with certain center-stabilizing potentials is in the confined phase at small S1, and we can study confinement analytically using the semiclassical methods. Extending the theories with adjoint scalar fields, we show that there is a new type of confined phase and that the topological objects in this phase generalize BPS and KK monopoles, which are constituents of instantons. I will also argue how one may be able to take the theory at large R3 X S1 by the Poisson resummation.

Jun 11 2013

Uni Wien

Valentina Verduci
(Uni Graz)

Pion-Nucleon scattering in Lattice QCD

Abstract: We investigate the S-wave pion-nucleon scattering in lattice QCD, in order to obtain new information on the negative sector of the nucleon spectrum. This approach enables us to shed some light on the nucleon excited states and can be generalized to the study of other sectors of the QCD spectrum.

Jun 18 2013

TU Wien

Paul Tiwald
(TU Wien)

From single atoms to solids - Quantum chemistry in solid state physics

Abstract: I will give an introduction to quantum chemistry methods and their application to solid state and surface physics within the embedded cluster approach. Two topics currently under investigation will be presented. The first topic is the F-center in Lithium Fluoride (LiF), a point defect giving rise to bound electronic states. The second topic is the interaction dynamics and the charge transfer of a proton approaching a LiF surface.

Jun 25 2013

Uni Wien

Harold Steinacker
(Uni Wien)

From Matrices to Quantum Geometry

Abstract: Based on simple examples of quantized spaces described in terms of matrices, we explore the idea that physical space-time might be described in terms of similar quantum spaces and quantum geometry. The emphasis of this talk is to explain how geometry can arise from matrices, based on the analogy with quantum mechanics.

Program Winter Semester 2012/2013

Program Summer Semester 2012

Program Winter Semester 2011/2012

Program Summer Semester 2011