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


Oct 9 2012

Uni Wien

Jan Rosseel
(TU Wien)

Massive gravity : problems and recent solutions.

Abstract: In this talk, I will give an overview of recent developments in massive gravity. After motivating massive gravity and discussing the well-understood linearized theory, I will mention various obstacles that have to be overcome in order to construct non-linear theories of massive gravity. I will then discuss various 'solutions' to some of these problems and an outlook on possible future directions.

Oct 16 2012

TU Wien

Jochen Zahn
(Uni Wien)

Perturbative algebraic quantum field theory and the quantization of submanifold embeddings

Abstract: We review the framework of perturbative algebraic quantum field theory, which provides a mathematically rigorous formulation of perturbative quantum field theories and allows for a generalization to curved spacetimes. We present a recent application of the framework, namely the perturbative quantization of embeddings of d-dimensional submanifolds into n-dimensional Minkowski space, based on the Nambu-Goto action. The model has the status of an effective field theory. We show the absence of anomalies for any dimensions d and n, so in particular, there is no critical dimension n for the case of string theory (d=2).

Oct 23 2012

Uni Wien

Sabina Alazzawi
(Uni Wien)

Integrable models in two-dimensional quantum field theory

Abstract: We give an overview of known results in the framework of local quantum physics. Possible generalizations are discussed and the connection of integrable models to deformations of QFTs is pointed out.

Oct 30 2012

TU Wien

Rafael Reiter
(TU Wien)

Tight-binding description of graphene: edges, magnetic fields and substrates.

Abstract: The experimental realization of graphene has opened a rapidly developing new field of fundamental and applied physics. Concerning the theoretical description of the electronic structure, the tight-binding approximation has the advantage that it can describe extended graphene systems with millions of atoms and magnetic fields, electric fields, substrates and disorder. After a review of the tight-binding formalism and its applications, the talk will focus on magnetic fields and the exact description of substrates and edges.

Nov 6 2012

Uni Wien

Katharina Doblhoff-Dier
(TU Wien)

The molecules' dance in laser light

Abstract: When atoms and molecules are subjected to intense light, all electrons and cores start moving in the laser's electric field. Today, laser-fields can be made so short and so intense and are so well controllable that experimentalists have started to explore the possibility to control the molecules movement by shaping the light fields. However, in many cases, the underlying  mechanisms are not yet understood and the analysis is difficult since "slow" processes such as vibrational and rotational dynamics are governed by much faster electronic processes. Yet, thorough understanding of the molecular processes triggered by the laser interaction is necessary if we want to control the molecules' dynamics in laser light. In this talk, I will give an introduction on how molecules interact with laser light, and how this can be described theoretically. In two examples from my work - the laser induced fragmentation yield of C2H22+ and the ionization of H2+ - , I will demonstrate how we can disentangle control mechanisms and attribute reactions to various molecular processes.

Nov 13 2012

TU Wien

! Canceled !

! Canceled !

Abstract: TBA

Nov 20 2012

Uni Wien

! Canceled !

! Canceled !

Abstract: TBA

Nov 27 2012

TU Wien

Hannes Grimm-Strele
(Uni Wien)

Challenges in Numerical Simulations of Astrophysical Flows

Abstract: Recent progress in multi-dimensional modelling of stars shows that the traditional one-dimensional approach is not sufficient to properly describe the structure of the star. Due to the wide range of length and time scales involved and the mixed hyperbolic-parabolic character of the governing equations these simulations are very difficult and expensive to carry out. Insufficient resolution gives qualitatively wrong results and numerical schemes of low order are not efficient. Boundary conditions have a large influence on the solution and must be designed suitably. Finally, the numerical grid must stay simple (i.e., structured) such that high-order methods are applicable, but must also offer some flexibility to cover more complicated domains. The simulation code ANTARES which is developed at the Faculty of Mathematics of the University of Vienna is designed to face these problems and will be presented in this talk together with some results and applications in stellar surface convection.

Dec 4 2012

Uni Wien

Sanjin Benic
(Zagreb University)

Phase diagram and the Equation of State for the covariant chiral quark models

Abstract: Models of QCD are still very much welcome not only to try and interpret latticedata, but also provide insight into the (presently) unaccessible territory. Amongst these, the non-local version of the Nambu Jona-Lasinio (nlNJL), supplemented by the Polyakov loop, is able to keepcontact with the lattice in the sense of the strong infrared running of the quark propagator invariants. We outline the QCD phase diagram in these studies, and the Equation of State as is relevant not only for lattice comparison but also, for example, the hydrodynamical calculations of the properties of the quark gluon plasma generated in heavy ion collisions, or the possible quark matter deep in the cores of neutron stars.

Dec 11 2012

TU Wien

Arjun Bagchi
(Edinburgh University)

Understanding Holography

Abstract: The formulation of a quantum theory of gravity remains one of the principle challenges of theoretical physics today. The holographic principle is a unique route to address this problem. It relates a theory of gravity to a theory without gravity in one lower dimension thereby paving the way for "understanding gravity without gravity". In my talk, I present an introduction to this intriguing principle. The studies of the holographic principle has been mainly confined to Anti de Sitter spacetimes though the celebrated AdS/CFT correspondence. After mentioning this briefly, I go on to my own work which describes how one should formulate holography for the more physically relevant flat spacetimes. Our discussions would be principally based on symmetries. We will formulate flat holography as a limit of usual AdS/CFT and derive some very surprising and interesting results for 3d flat spacetimes.

Dec 18 2012

Uni Wien

Christian Köhler
(Uni Wien)

Infinite Spin Representations: Geometry and Quantum Fields

Abstract: A recent construction, relating Wigner representations of positive mass to those of infinite spin in a continuous way by using stereographic projection, is presented. In this way all transformations of a particle's internal degrees of freedom assume the form of subgroups of the Möbius group, while its mass is related to the inverse radius of the Riemann sphere. We will relate our findings to the construction of intertwiners in the infinite spin limit.

Jan 8 2013

TU Wien

Daniel Nagaj
(Uni Wien)

Entanglement without Frustration

Abstract: How much entanglement can there be in a ground state of a simple 1D system with local interactions? Critical behavior (e.g. long-range correlations) is usually associated with frustration. When a system is unfrustrated (all local Hamiltonian terms are minimized), we expect the ground state to be simple. While this holds for qubits, things are quite different for higher-spin particles (already for qutrits). We'll talk about a state made from well bracketed words and look at the proof of its high entanglement entropy scaling and a lower bound of the Hamiltonian using congestion in graphs, parenting trees, many uses of the projection lemma and other fun stuff.

Jan 15 2013

Uni Wien

Jürgen Klepp
(Uni Wien)

! Canceled !

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.

Jan 22 2013

TU Wien

Nele Callebaut
(Ghent University)

Holographic study of magnetically induced rho meson condensation

Abstract: In the presence of strong magnetic fields, the QCD vacuum may become unstable towards condensation of charged rho mesons, forming a superconducting state. I will talk about our investigation of this possible instability in a well-known holographic QCD model called the Sakai-Sugimoto model, using 2 flavours and taking into account the chiral magnetic catalysis effect. Rho meson condensation occurs in this model at very high values of the magnetic field, eB approximately 0.8 GeV^2, possibly present during the cosmological electroweak phase transition or in heavy ion collisions at the LHC.

Jan 29 2013

Uni Wien

Ilse Krätschmer, Valentin Knünz
(HEPHY Wien)

Higgs searches at the LHC - observation of a new boson with a mass of 125 GeV

Abstract: The 4th of July 2012 was a joyous day for the high energy physics community. The two LHC-experiments, ATLAS and CMS, announced the discovery of a new boson which is consistent with the Standard Model Higgs boson, with a mass of around 125 GeV. This discovery was also pronounced the breakthrough of the year 2012.This talk introduces the Standard Model, the Higgs-mechanism, and presents the results of the CMS and ATLAS searches for the Standard Model Higgs boson, with an emphasis on the descripiton of the experimental setup of the Higgs-searches at CMS.

Program Summer Semester 2012

Program Winter Semester 2011/2012

Program Summer Semester 2011

Program Winter Semester 2010/2011