Vienna Theory Lunch Seminar

by Iva Lovrekovic (VUT), Max Riegler (VUT), Jakob Salzer (VUT),
Thomas Moser (UV) and Peter Poier (UV)

Tuesdays 12:15-13:30

held alternatively at:

Vienna University of Technology (VUT): Wiedner Hauptstr. 8-10, yellow area, 10th floor, seminar room E136

University of Vienna (UV): 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) 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).

Wie kann ich teilnehmen?

How can I join?

Einfach erscheinen! Um per Email informiert zu werden, bitte in die Mailinglist eintragen oder Mail an albert.georg.passegger at schicken

Just attend! To receive informations via email go to the Mailinglist or drop an email to albert.georg.passegger at


Mar 4 2014


Natascha Riahi
(University of Vienna)

Can time be saved in quantum cosmology?

Abstract: I will discuss the problem of time in quantum cosmology and present a possible time evolution for Minisuperspaces.

Mar 11 2014


Matthias Ihl
(Universidade do Porto)

Holographic zero sound at finite
temperature in the Sakai-Sugimoto model

Abstract:  I will discuss some recent work concerning the existence and properties of zero sound in the Sakai-Sugimoto model at finite
temperature (and large baryon density). After reviewing some background on Landau's Fermi liquid theory and the finite temperature
Sakai-Sugimoto model, I will present new results in this holographic framework, such as spectral functions, quasi normal modes and dispersion relations, and compare them to expectations from Fermi liquid theory and other holographic models.

Mar 18 2014


Dinyar Rabadi

Upgrade of the Global Muon Trigger for the CMS Experiment at the LHC

Abstract: The Level-1 Trigger for the Compact Muon Solenoid (CMS) experiment with an emphasis on the Global Muon Trigger (GMT). I will then detail the planned upgrades to this system for the Large Hadron Collider (LHC) run period beginning in 2015. Finally I will introduce one of the analyses that could significantly benefit from this upgrade.

Mar 25 2014


Maria Irakleidou
(Vienna University of Technology)

Conformal gravity holography in four dimensions

Abstract: We formulate four-dimensional conformal gravity with (Anti-)de Sitter boundary conditions that are weaker than Starobinsky boundary conditions, allowing for an asymptotically subleading Rindler term concurrent with a recent model for gravity at large distances. We prove the consistency of the variational principle and derive the holographic response functions. One of them is the conformal gravity version of the Brown-York stress tensor, the other is a `partially massless response'. The on-shell action and response functions are finite and do not require holographic renormalization. Finally, we discuss phenomenologically interesting examples, including the most general spherically symmetric solutions and rotating black hole solutions with partially massless hair.

Apr 1 2014


Silvano Ferrari
(Vienna University of Technology)

Analogies between Soft Matter Systems and Manner Schnitten

Abstract: Patchy colloids are a model system introduced to model anisotropic interactions in colloidal dispersion. After a brief introduction on the topic, we introduce Inverse Patchy Colloids, and show our study of the phase diagram, which reveals structures similar to the famous viennese sweets.

In the second part, the integral equation approach to the liquid state theory is briefly summarized, and it is shown wie it can be used to avoid time-consuming simulations, and how we are trying to improve it.

Apr 8 2014


Ingo Kirsch
(DESY Hamburg)

Holography of the chiral magnetic effect and anisotropy in heavy ion collisions

Abstract: The chiral magnetic effect (CME) is a highly discussed effect in heavy-ion collisions stating that, in the presence of a magnetic field B, an electric current is generated in the background of topologically nontrivial gluon fields. We present a holographic (AdS/CFT) description of the CME in terms of a fluid-gravity model which is dual to a strongly-coupled plasma with multiple anomalous U(1) currents. In the case of two U(1) charges, one axial and one vector, the CME formally appears as a first-order transport coefficient in the vector current. We will holographically compute this coefficient at strong coupling and compare it with the hydrodynamic result. Finally, we will discuss an anisotropic variant of the model and study a possible dependence of the CME on the elliptic flow coefficient v_2.

Apr 15 2014


Thomas Zojer
(University of Groningen)

The non relativistic superparticle

Abstract: I will give a short introduction to supersymmetry and explain what we understand by non-relativistic supersymmetry. This will lead to a notion of non-relativistic supergravity which I will use to construct the action of a (super) point-particle. Finally, I will discuss different gaugings of this action to describe a point-particle in backgrounds with different symmetries; from the Galilean point-particle to the Newton--Cartan point-particle.

Apr 22 2014

Easter holidays

Easter holidays

Apr 29 2014


Markus Stana
(University of Vienna)

Using brilliant X-ray sources to uncover atomic-scale migration models -- an introduction to aXPCS

Abstract: Advances of Synchrotron sources in the last two decades made it possible to expand Dynamic Light Scattering to the X-ray regime. In recent years our group explored the limits of this technique by using it to study diffusion on the atomic scale. This talk will give an introduction to atomic-scale X-ray Photon Correlation Spectroscopy and discuss how coherent X-rays can give a picture of reals space circumventing the phase problem. Selected diffusion mechanisms will be exemplified and compared with experimental data.

May 6 2014


Markus Wallerberger
(TU Wien)

Why three is close to infinity and two is much greater than one

Abstract: In condensed matter systems with strong electronic correlations, the familiar picture of a non-interacting electron cloud breaks down. These materials show facinating "emergent" phenomena. However, the breakthrough in treating many of such systems numerically only came in the 1990s with the advent of dynamical mean field theory (DMFT) [1] and related in ab-initio approaches like LDA+DMFT [2].
DMFT is formulated in terms of the one-particle many-body propagator, the Green's function. Its two-particle counterparts, the vertex functions, have remained largely uncharted territory until recently. However, they are interesting from both a physical and a modelling perspective: vertex functions enter as vertex corrections into the system's response functions (such as the spin susceptibility); their divergencies mark bifurcation points of the system [3]; and they are the central ingredient to most diagrammatic extensions of DMFT [4].
Due to their two-particle nature, vertex functions are both huge in size and rich and non-trivial in structure, which makes them difficult to access by numerical methods such as continuous time quantum Monte Carlo (CT-QMC) [5]. We show that only by a deep understanding of the diagrammatics, asymptotics and symmetries, one can overcome these hurdles. We then turn to the moderatly correlated FeAl alloy and use vertex functions to study the formation and screening of local moments in this compound to explain the absence of magnetic order.

 [1] A Georges et al. - Rev. Mod. Phys. 68, 13-125 (1996)
 [2] K Held et al. - J. Phys. Condens. Matter 20 064202 (2008)
 [3] T Schäfer et al. - Phys. Rev. Lett. 110, 246405 (2013)
 [4] e.g., A Toschi et al - Phys. Rev. B 75, 045119 (2007)
 [5] E Gull et al. - Rev. Mod. Phys. 83, 349 (2011)

May 13 2014


Piotr Pietrulewicz
(University of Vienna)

Variable flavor number schemes in QCD

Abstract: In this talk I will illustrate how to include heavy quark effects in QCD processes with various dynamical scales. The resulting mass factorization theorems resum all large logarithms and can account for arbitrary hierarchies between the mass scale and the kinematic scales. Specific examples covered are the hadronic R-ratio, deep-inelastic scattering and event shapes.

  May 20 2014


Anna Galler
(TU Wien)

Materials with strong electronic correlations: The LDA+DMFT approach

Abstract: Calculating electronic properties of materials is an important task in solid state theory. A powerful tool to perform electronic structure calculations is density functional theory in its local density approximation (LDA). However, LDA fails if electronic correlations are strong. On the other hand, the dynamical mean field theory (DMFT) can deal with strongly correlated model Hamiltonians. In this talk I will explain how LDA and DMFT can be combined in order to perform realistic calculations for strongly correlated materials and I will show some preliminary results for the materials I am currently working on.

May 27 2014


 Gunther Cronenberg
(Atominstitut Vienna)

qBounce: Frequency's view on Newton's Inverse Square Law of Gravity

Abstract: In the frame of the qBounce experiment, resonant transitions between several of the lowest quantum states of gravitationally bound neutrons are observed for the first time. The coupling between the states is provided by well-defined mechanical oscillations of neutron mirrors. The presented spectroscopy method enables a frequency's view on Newton's Inverse Square Law of Gravity, which has been put under scrutiny by theoretical extensions of the Standard Model. As yet undiscovered particles of dark matter or dark energy would introduce a measurable energy shift, we can present experimental limits for dark-energy chameleons fields and the pseudo-scalar interaction of an axion, a prominent dark matter particle.

June 3 2014


Arjun Bagchi
(IISER Pune and TU Wien)

One Symmetry to Rule Them All

Abstract: I outline the various apparently different problems which can be dealt with the symmetries of the Galilean Conformal Algebra. These include applications to flat holography, non-relativistic physics and the tensionless limit of string theory.

June 10 2014


Clemens Moritz 
(University of Vienna)

Periodic Boundary Conditions and their Effects on the Simulation of Drops

Abstract: The use of periodic boundary conditions is a common trick used when doing molecular simulations on the computer. After a short introduction of this technique, we look at the effect it has on the simulation of droplets in a simulation box which is the emergence of so called geometric phases that are characterized by droplet shapes other than spherical. Transitions between these phases have been observed to be responsible for exponential slowing down in simulations[1] and hence we will try characterize them by finding a suitable order parameter.
[1] T. Neuhaus and J. S. Hager, J. Stat. Phys. 113, 47 (2003).

June 17 2014


Marco Schreck
(Indiana University)

Violation of Lorentz invariance, related phenomena, and experiments

Abstract: In the past 15 years the search for a possible violation of Lorentz invariance has become one pillar in fundamental research. This talk will give an introduction to this hot and fascinating topic. First of all it will be motivated why Lorentz symmetry may be violated in the vicinity of the Planck scale. As a next step an effective framework, which describes Lorentz violation for energies much smaller than the Planck scale, shall be introduced. The latter is known as the Standard-Model Extension whose Lagrange density includes all terms consistent with the ordinary Standard Model (plus gravity) but violating Lorentz invariance. This will lead us to possible phenomena that occur in this context such as vacuum birefringence. The last part of the talk will be dedicated to examples for experiments that are used to search for Lorentz violation in nature.

June 24 2014


Fabian Lackner 
(Vienna University of Technology)

Solving the time-dependent many-body problem without wavefunctions

Abstract: The theoretical description of correlated quantum many-body systems is one of the major challenges in current physics. Quantum correlations occur at practically all levels of complexity: from multi-photon ionization of atoms to high temperature superconductivity in solids. In general, the amount of information stored in the wavefunction makes it inaccessible to analytical or even numerical calculations. However, many dynamical observables including the energy are completely defined by the reduced two-particle density matrix. Recently a method has been developed to calculate the ground state energy of complex molecules based on the two-particle density matrix without knowledge of the full wavefunction. In this talk i will present a time-dependent version of this theory. As a testing ground we use the lithium hydrate molecule in high intense laser fields. The accuracy of the newly developed theory is benchmarked against the multiconfigurational time-dependent Hartree-Fock method.

Program Winter Semester 2013

Program Summer Semester 2013

Program Winter Semester 2012 2012/2013

Program Summer Semester 2012

Program Winter Semester 2011/2012