Vienna Theory Lunch Seminar

by Christian Ecker (VUT), Alexander Haber (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.

Mar 10 2015


Pascal Anastasopoulos
(Vienna University of Technology)

String Phenomenology

Abstract: D-brane realizations of the Standard Model predict new particles and couplings. In this seminar we will focus on a) anomalous Z's gauge bosons and b) excited states for each matter field of the SM. If the string scale is low (at a few TeV range), such particles can be visible at the LHC.

Mar 17 2015


Kyrylo Simonov
(University of Vienna)

Is quantum linear superposition exact on all energy scales? A unique case study with flavour oscillating systems

Abstract: Quantum mechanics, in its standard formulation, gives an extremely accurate description of microscopic systems and, up to date, no experiment has found any contradictions to its predictions. However, the quantum theory meets some conceptual difficulties with macroscopic systems: the principle of linear superposition, which is a corner stone of quantum theory, conflicts our everyday experience: Why for instance, a table or cat is never found to be in two places at the same time? And how does a measurement process break the superposition of microscopic systems? Models of spontaneous collapses, so called collapse models, provide a powerful, mathematical complete approach to preserve quantum linearity at the microscopic level while breaking it on the macroscopic level and giving new predictions in the region in-between. This is achieved by modelling the reduction of the wave function as a physical process. A highly attractive property of such models is that they can be excluded experimentally e.g. via modern ongoing matter wave interferometry or via under ground X-ray experiments. This talk gives an introduction to collapse models and the idea behind. Then it outlines how neutral flavour oscillating K-mesons, being superpositions of two different mass-eigenstates, can uniquely contribute to the testing of collapse models.

Mar 24 2015


Vicent Mateu
(University of Vienna)

Recent progress in massless and massive event shapes

Abstract: In this talk I will give an overview of our recent developments in the theoretical description of the event shapes, and will discuss the results obtained in recent analyses for the determination of the strong coupling constant. In the massless case I will focus on thrust and C-parameter, showing results for resummation at N3LL order plus three-loop matrix elements, and the analytic treatment of power corrections. As for massive event shapes, I will discuss the novel theoretical treatment of secondary radiation of massive quarks, and also the challenges to incorporate primary production.

Apr 14 2015


Sandra Eibenberger
(University of Vienna)

Matter-wave interference and quantum-assisted metrology with large organic molecules

Abstract: Matter-wave interferometry can be used to probe the foundations of physics and to enable precise measurements of particle properties and fundamental constants. Quantum interference experiments with large molecules have enabled studies of the quantum superposition principle with particles of increasing mass and complexity. Kapitza-Dirac-Talbot-Lau interferometry [1] has enabled quantum experiments with a wide variety of macromolecules, even using particles with a mass exceeding 10 000 amu [2]. These experiments define the currently most stringent bound of the experimental macroscopicity parameter for quantum superpositions [3]. Typical de Broglie wavelengths of the investigated particles are in the order of 0.3-5 pm. This is significantly smaller than any molecular extension (nanometers) or the delocalization length in our interferometer (hundreds of nanometers). Many vibrational and rotational states are populated since the molecules are thermally highly excited (300-1000 K). And yet, high-contrast quantum interference patterns could be observed. The visibility and position of these matter-wave interference patterns is highly sensitive to external perturbations. This sensitivity has opened the path to extensive studies of the influence of internal molecular properties on the coherence of their associated matter waves. In addition, it enables a new approach to quantum-assisted metrology. I describe how KDTL interferometry can be used to investigate a number of different molecular properties, including electric moments [4] and optical absorption cross sections [5].

[1] Gerlich, S., et al., A Kapitza-Dirac-Talbot-Lau interferometer for highly polarizable molecules. Nat. Phys., 2007. 3(10): p. 711-715.
[2] Eibenberger, S., et al., Matter-wave interference with particles selected from a molecular library with masses exceeding 10 000 amu. Phys. Chem. Chem. Phys., 2013. 15: p. 14696-14700.
[3] Nimmrichter, S. and K. Hornberger, Macroscopicity of Mechanical Quantum Superposition States. Phys. Rev. Lett., 2013. 110: p. 160403-160403.
[4] Eibenberger, S., et al., Electric moments in molecule interferometry. New J. Phys., 2011. 13: p. 43033-43033.
[5] Eibenberger, S., et al., Absolute absorption cross sections from photon recoil in a matter-wave interferometer. Phys. Rev. Lett., 2014. 112: p. 250402-250402.

Apr 21 2015


Andreas Goudelis

Aspects of simple dark matter models

Abstract: Over the last few decades, the evidence that some relatively non-luminous form of non-baryonic matter ("dark matter") is dominating the matter content of the universe has piled up. However, essentially all arguments for the existence of dark matter are of a gravitational nature and little is known about its non-gravitational properties. I will present a few simple models of particle dark matter and discuss some of their aspects, in particular related to the questions of the dark matter abundance in the universe and its non-gravitational detection strategies.

Apr 28 2015


Timm Wrase
(Vienna University of Technology)

Dark Energy and Inflation

Abstract: Roughly 70% of the energy density of our current universe is in the form of so called dark energy. While we do not exactly know what this dark energy is, we know that it behaves almost identical to a positive cosmological constant and is responsible for the observed accelerated expansion of our current universe. We also have ample evidence that our very early universe underwent a short period of accelerated expansion that is called inflation. Inflation is sensitive to corrections that cannot be calculated within general relativity coupled to field theory. So in order to understand such corrections we need a UV complete theory of quantum gravity. I will review attempts to construct models that account for the early and late time accelerated expansion of our universe in the context of string theory, which is currently our only contender for a theory of everything.

May 5 2015


Emanuele Locatelli
(University of Vienna )

Dynamical properties of passive and active particles in Single File

Abstract: Diffusive passive particle, like colloids, as well as active particles, including bacteria and algae, may happen to be confined in channels so narrow that they cannot overtake each other (Single File conditions). This interesting situation, relevant in Biology, Nanotechnology as well as for water purification and filtration issues, reveals nontrivial physical features as a consequence of the strong inter-particle correlations developed in collective rearrangements. We study the dynamical properties of active and passive hard particles under Single File conditions. We propose to sort active particles in two categories: Runners and Tumblers, depending on whether their motion is dominated by straight runs or changes of the directions, respectively. Whereas tumblers’ dynamical behavior reproduces passive (diffusive/Brownian) motion paradigms, runners arrange into clusters which are continuously merging and splitting (living clusters). Finally, in the presence of two absorbing boundaries , by means of analytical techniques, numerical simulations and experiments performed in microfluidic devices, we study the emptying process of the Single File system, i.e. we characterize the progressive decrease of the number of particles, absorbed at the boundaries.

May 12 2015


Jakob Salzer
(Vienna University of Technology)

Two-dimensional Dilaton Gravity - A Toy Model for Gravity

Abstract: The study of conceptual problems in gravity is often hindered by the technical complexities of general relativity in four dimensions. In such cases it is convenient to have a toy model at one’s disposal that captures the relevant features of general relativity while reducing technical difficulties to a minimum. Two-dimensional dilaton gravity is such a model. In this talk I will introduce two-dimensional dilaton gravity, describe some of its appealing features and report on some recent work on thermodynamics in this framework.

May 19 2015


Josef Pradler

Light super-WIMPs in Astrophysics and Experiment

Abstract: More often than not, astrophysical probes are superior to direct laboratory tests when it comes to light, very weekly interacting particles, and it takes clever strategies and/or ultra-pure experimental setups for direct tests to be competitive. In this talk, I will highlight this competition on the example of a simple extension of the Standard Model, "Dark Photons." They are a dark matter candidate, and we show how direct detection probes can be superior to stellar constraints. When they decay, cosmology may offer the best sensitivity.

Jun 2 2015


Paul Mezgolits
(Vienna University of Technology)

An introduction to inflation, and how this might work in conformal gravity

Abstract: The big bang theory is our best description of the observed universe. Despite its succeses it can not adress key features of the cosmos like the homogeneity and isotropy of our universe and the tiny deviation from this behaviour. The theory of cosmic inflation adresses these issues. My talk will first motivate, and then give a short introduction to, the theory of inflation followed by a discussion of a model of inflation that is based on a theory of gravity that is different from standard Einstein gravity. While inflation is an application of general relativity and quantum field theory, my talk aims to describe the big picture and is accesible to an audience familiar with special relativity and quantum mechanics.

Jun 9 2015


Friedrich Schöller
(Vienna University of Technology)

Heat Kernels and Quantum Gravity

Abstract: I give a short introduction to the path integral formulation of quantum mechanics and show how the heat equation can be used to study the semiclassical approximation of a quantum theory. The methods introduced are used to obtain thermodynamic quantities of a three dimensional toy model of quantum gravity.

Jun 16 2015


Marco Battiato
(Vienna University of Technology)

From the discovery to the control of THz spin currents: towards ultrafast spintronics

Abstract: The debate over the origin of the ultrafast demagnetization [1] has been intensively active for the past 16 years. Several microscopic mechanisms have been proposed but none has managed so far to provide direct and incontrovertible evidences of their validity. In this context I have proposed an approach based on spin dependent electron diffusion as the driver of the ultrafast demagnetization [2]. Recent experimental findings have revolutionized the field by confirming the existence of spin superdiffusion. We have shown that 1) spin diffusing away from a layer undergoing ultrafast demagnetization can be used to create an ultrafast increase of magnetization [3] in a neighboring magnetic layer, 2) optical excitation is not a prerequisite for the ultrafast demagnetization [4] and that spin unpolarised electrons superdiffusing into a ferromagnetic layer can trigger ultrafast demagnetisation, and 3) superdiffusive spin currents can be tailored by appropriate choice of materials and used to produce broadband THz emission via the inverse spin Hall effect [5]. The impact of these new discoveries goes beyond the solution of the mystery of ultrafast demagnetization. It shows how spin information can be, not only manipulated, as shown 16 years ago, but most importantly transported at unprecedented speeds. This new discovery lays the basis for femtosecond spintronics.

[1] E. Beaurepaire, J.-C. Merle, A. Daunois, J.-Y. Bigot, Phys. Rev. Lett., 76, 4250 (1996).
[2] M. Battiato, K. Carva, P.M. Oppeneer, Phys Rev. Lett. 105, 027203 (2010).
[3] D. Rudolf,* C. La-O-Vorakiat,* M. Battiato,* R. Adam, J. M. Shaw, E. Turgut, P. Maldonado, S. Mathias, P. Grychtol, H. T. Nembach, T. J. Silva, M. Aeschlimann, H. C. Kapteyn, M. M. Murnane, C. M. Schneider, and P. M. Oppeneer, Nature Comm. 3, 1037 (2012).
[4] A. Eschenlohr,* M. Battiato,* P. Maldonado, N. Pontius, T. Kachel, K. Holldack, R. Mitzner, A. Föhlisch, P. M. Oppeneer, and C. Stamm, Nature Mater. 12, 332 (2013).
[5] T. Kampfrath, M. Battiato, P. Maldonado, G. Eilers, J. Nötzold, I. Radu, F. Freimuth, Y. Mokrousov, S. Blügel, M. Wolf, P. M. Oppeneer, and M. Münzenberg, Nature Nanotechnol. 8, 256 (2013).

Jun 23 2015


Suchita Kulkarni

BSM/SUSY phenomenology at the LHC

Abstract: The 7 and 8 TeV Run1 of the LHC has brought to us the discovery of a Higgs boson and plethora of results for Beyond the Standard Model (BSM) searches. Even if there has been no evidence of BSM so far, these results are crucial in constraining the parameter space of BSM scenarios. In this talk, I will take a survey of the current existing direct and indirect constraints on Supersymmetry from the LHC and the efforts in the theory world to use these constraints systematically and effectively. I will further illustrate with some case studies, the conclusions that can be derived for SUSY parameter space after LHC Run1.

Jun 30 2015


Georg Rohringer
(Vienna University of Technology)

Critical Properties of Strongly Correlated Many-Electron Systems -- A Dynamical Vertex Approximation Study

Abstract: Strongly correlated many-electron systems exhibit a large number of fascinating physical phenomena, such as correlation driven insulating phases, magnetism or high-temperature superconductivity. At the same time, a theoretical description of these systems turns out to be considerably difficult. Hence, one has to adopt approximations in order to calculate experimentally accessible quantities for such systems. In my talk I will introduce the basic models and techniques for treating strong correlations theoretically and describe some of the state-of-the-art approximations for solving the many-body problem in this framework. In particular, I will explain how the dynamical mean field theory (DMFT) describes local correlation effects in a lattice exactly. Since in many physical situation also nonlocal correlations play an important role extensions of DMFT are needed. One of such extensions is the Dynamical Vertex Approximation (D$\Gamma$A), which I will introduce. Its applicability for treating strongly correlated electro

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