Vienna Theory Lunch Seminar

by Iva Lovrekovic (VUT), Jakob Salzer (VUT),
David Hämmerle (UV), Moritz Preisser (UV) and Daniel Samitz (UV)

Tuesdays 12:15-13:30

held alternately 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

We thank our kind sponsors:

Dean of physics, TU

Dean of physics, UV

Daniel Grumiller, TU



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 Beginn des Masterstudiums dem Vortrag folgen kann. BachelorstudentInnen können besonders von dem Seminar profitieren, da es ihnen ermöglicht einen Eindruck in die Forschungsarbeit beider Universitäten zu erhalten. Die Vortragenden werden dabei auch ermutigt darüber zu sprechen, warum sie ein gewisses Forschungsgebiet gewählt haben. Dabei dürfen durchaus offene Fragen und Probleme behandelt werden und es ist nicht notwendig einen Vortrag über eine "perfekte", abgeschlossene Arbeit zu halten.

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. Undergraduate 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 Mailingliste eintragen.

Just attend! To receive informations via email register for the Mailinglist.

Oct 7 2014


Stefan Prohazka
(Vienna University of Technology)

Higher spins and Lifshitz holography with isotropic scale invariance

Abstract: I will give an overview on higher spin theories in three and four dimensions and present interesting open questions. Furthermore I will answer the question if it is possible for an anisotropic Lifshitz critical point to exhibit isotropic conformal invariance by showing a concrete holographic realization.

Oct 14 2014


Bahman Dehnadi
(University of Vienna)

Charm and Bottom mass determinations from relativistic QCD sum rules at four loops

Abstract: In this talk I will present our recent results on charm and bottom mass determinations based on perturbative QCD with a thorough analysis of theoretical uncertainties.

Oct 21 2014


Christian Ecker
(Vienna University of Technology)

Numerical Holography

Abstract: In recent years numerical holography (numerical relativity + AdS/CFT) has developed to a powerful tool for studying the dynamics of strongly coupled systems. I will review applications of this method to the non-equilibrium dynamics of heavy ion collisions and to the computation of entanglement entropy.

Oct 28 2014


Magdalena Zych
(University of Vienna)

Gravitational time dilation in quantum mechanics — for feasible tests of the quantum-and-gravity interplay

Abstract: Quantum mechanics and general relativity have been extensively confirmed in many experiments but still all tests of the influence of gravity on quantum systems remain fully consistent with the non-relativistic, Newtonian gravity. Rapidly developing quantum technologies allow for quantum experiments with increasingly complex systems. The regime where general relativity affects internal dynamics of such systems is just becoming available for experimental exploration and is likely to allow for first feasible tests of the interplay between quantum mechanics and general relativity. This talk will give an overview of new physical effects in this regime, in particular, resulting from the time dilation. These include new effects in interference of composite quantum systems and a universal decoherence mechanism affecting center of mass of all composite systems (with an internal energy spread). Moreover, in order to verify whether the phenomenon of gravity is indeed tantamount to space- time geometry, in this regime novel experiments are necessary. For a geometric picture of gravity to hold, there must be a strict equivalence between the rest mass-energy of the system, the mass-energy that constitutes its inertia, and that constitutes its weight. In quantum mechanics internal energy of the system is given by a Hamiltonian operator and therefore this equivalence has to be satisfied by the entire rest, inertial and gravitational mass-energy operators. In classical physics, the equivalence is only required between the mass-energy values. Thus, validity of the geometric picture of gravity in classical physics does not guarantee its validity in quantum mechanics, which thus requires an independent verification. I will introduce an effective (low-energy) test-theory, suitable to incorporate the above quantum formulation of the equivalence conditions, discuss new and sketch how it can be tested.

Nov 4 2014


Wout Merbis
(Vienna University of Technology)

Massive Gravity and Holography in Three Dimensions

Abstract: Modifications of General relativity (GR) have been a longstanding research problem. Motivated by cosmological observations, one specific modification of GR deals with assigning a small mass to the graviton, the force carrier of gravity. The resulting theory of massive gravity must be constructed in a careful way to avoid unphysical propagating degrees of freedom. Beside giving a general overview on this problem, the topic of this talk is to discuss the construction of a general class of three dimensional massive gravity models which steers clear of many pathologies found in previous models, in particular in relation to the holographic duality.

Nov 11 2014


Georg Wachter
(Vienna University of Technology)

Ultrafast electron dynamics in condensed matter

Abstract: Control of electron motion by external electric fields or voltages lies at the heart of modern electronics. While transistors operate on timescales in the picosecond regime, the fastest electronic processes in solids can be many orders of magnitude faster on the (sub)-femtosecond time scale. In recent years, the ability of modern laser technology to custom-tailor strong time-dependent optical electric fields has enabled unprecedented observation and control of electron motion in solids on the ultrafast time scale. Such strong field interaction with condensed matter promises light-field electronics devices operating on the femtosecond time and nanometer length scale. Its theoretical exploration faces the challenge to simulate the time-dependent many-electron problem. We will briefly introduce the goals and building blocks of ultrafast physics. We then illustrate recent progress in the description of ultrafast electron dynamics in condensed matter with the help of two examples. Metal nano-tips illuminated by few-cycle laser pulses become ultrafast electron emitters and the laser pulse steers the electron motion near the nano-structure. In large band-gap dielectrics such as quartz glass (SiO2), intense optical laser pulses can induce electron tunneling between neighboring atoms, leading to the efficient generation of quasi-free carriers and a femtosecond transition from an insulator to a metal. Ab-initio simulations based on time-dependent density functional theory are found in good agreement to first experimental data and allow us to see and understand the electron motion on the atomic length and time scales.

Nov 18 2014


Peter Poier
(University of Vienna)

Effective Interactions for Colloids and Polymers in Soft Matter systems

Abstract: In Soft Matter Physics we work with macromolecules like colloids or polymer chains. Instead of an atomistic description we often use a coarse-grained approach where the state of these large particles is described with an effective model that involves much less degrees of freedom. The main advantage of effective models is that they are computationally cheaper and in addition they facilitate an intuitive understanding of the Physics described. Another nice property of Soft Matter Systems is that the interactions in the effective model can be tuned easily by changing only the properties of the solvent (e.g. by adding salt). I will give some examples for interesting effective models in Soft Matter Physics. In particular I will introduce an effective model that leads to so called Cluster Crystals, which are a novel and interesting state of matter. I will explain how this effective model is related to a system of semi-flexible ring polymers. In addition I will show recent results of simulations in which we monitor the localization probability of knots on polymer chains with heterogeneous rigidity under tension.

Nov 25 2014


Philip Schäffer
(University of Vienna)

How to get from the metric tensor to an Einstein-Vlasov System in 45 minutes

Abstract: A short introduction on some basic notions in GR like the metric tensor and topology of manifolds will be given. Furthermore an example for a cosmology will be given and its properties will be discussed.

Dec 2 2014


James Whitfield
(University of Vienna)

TDDFT: V-representability on lattices

Abstract: I will explain time dependent density functional theory and sketch our previous result concerning the computational complexity of solving the V-representability problem. I will talk about some more recent results concerning a numerical implementation of our scheme. The talk will only require familiarity with linear algebra.

Dec 9 2014


Franz Kerschbaum
(University of Vienna)

On-board intelligence for space telescopes

Abstract: Space telescopes with their more and more complex instrumentation require specialized on-board IT systems. This is to cope with both highly specialized and demanding operational modes as well as the enormous volumes of data produced. Severe computational, power, mass and volume constraints together with limited communication rates and autonomous operation make such space IT systems and the respective on-board SW quite demanding and often mission critical. Over the last 1.5 decades the Department of Astrophysics at the University of Vienna built up extensive expertise in this very field of on-board data processing and more general on-board instrument software. Together with national and international partners past, current and future space missions are provided with our systems, e.g. Herschel, Brite-Constellation, Cheops, Plato or Athena. Besides the technical aspects of our participations also a few astrophysical results and aims will be presented.

Dec 16 2014


Liang Si
(Vienna University of Technology)

The ferromagnetic metal to non-magnetic insulator phase transition in SrRuO3 ultrathin films

Abstract: Using density-functional theory plus dynamic mean field theory (DFT+DMFT) method, we investigated the correlation effects in ultathin films of 4d transition-metal oxide ferromagnetic metal SrRuO3. We found an intrinsic thickness limitation for preserving the ferromagnetism and metallicity: Single unit cell layer SrRuO3 becomes a robust insulator without ferromagnetism. Current experimental efforts such as strain and capping are hopeless towards the ferromagnetic ultrathin (single-layer) SrRuO3; they could effectively tune the crystal-field splitting between Ru t2g orbitals, but drive a transition only between distinct paramagnetic and antiferromagnetic insulating states.

Jan 13 2015


Andreas Schmitt
(Vienna University of Technology)

Neutron stars as a laboratory for fundamental physics

Abstract: I will review general aspects and latest developments of how neutron stars can constrain properties of dense nuclear and quark matter. I will discuss theoretical challenges in dense QCD matter, but mainly focus on astrophysical signals and how they can be related to fundamental physics.

Jan 20 2015


Elena Ginina

Lightest MSSM Higgs boson decay into a charm quarks pair at full one loop level with flavour violation

Abstract: We study lightest neutral Higgs decay to a pair of charm quarks in the MSSM at full one-loop level with non-minimal quark flavour violation (QFV). In the numerical analysis we consider mixing between the second and the third squark generations and the relevant constraints from B meson data are taken into account. It is shown that the full one-loop corrected decay width can be quite sensitive to the MSSM QFV parameters due to large scharm-stop mixing and large trilinear couplings. We summarise the theoretical and experimental errors and discuss the measurability of these SUSY QFV effects at the ILC.

Jan 27 2015


David Müller
(Vienna University of Technology)

Superfluid density in a relativistic fermionic superfluid

Abstract: In my talk I will discuss a field-theoretical model to describe a relativistic fermionic superfluid. Such superfluids are likely to be found in the cold dense matter inside neutron stars. I will talk about the mean-field approximation of the model and how to go beyond this approximation by introducing bosonic fluctuations. In particular I will show how to calculate the superfluid density in terms of Feynman diagrams.

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