Vienna Theory Lunch Seminar

by Olaf Krüger (UV), Marcus Sperling (UV), Philipp Stanzer (TU)
and David Toneian (TU)

Tuesdays 12:15-13:30

held alternately at:

TU Wien (TU): 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

Faculty 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 6 2018


Borivoje Dakic
(Institute for Quantum Optics and Quantum Information (IQOQI), Vienna)

Single-Copy Entanglement Detection

Abstract: A main focus of current practical quantum information research is on the generation of large-scale quantum entanglement involving many particles with the goal of achieving real applications of quantum technologies. An important instance of this challenge is the verification problem: how to reliably certify the presence of quantum resources, in particular quantum entanglement. The plausibility of standard verification schemes (for example, based on entanglement witnesses) is questionable, since they require repeated measurement on large ensemble of identically prepared copies, which is highly demanding to achieve in practice when dealing with large-scale entangled quantum systems. In this talk, I will present our recent work [1] where we develop a novel method by formulating verification as a decision procedure, i.e. entanglement is seen as the ability of quantum system to answer certain “yes-no questions”. We show that for a variety of large quantum states even a single copy suffices to detect entanglement with a high probability by using local measurements. For example, a single copy of a 24-qubit linear cluster state suffices to verify entanglement with more than 95% confidence. Our method is applicable to many important classes of states, such as cluster states or ground states of local Hamiltonians in general.
References: A. Dimic, and B. Dakic, “Single-copy entanglement detection”, arXiv:1705.06719 (2017).

Mar 13 2018


Olaf Krüger
(University of Vienna)

A basic introduction to the Hopf algebra of Feynman graphs

Abstract: I will give a blackboard talk to introduce the notion of a Hopf algebra at the example of Feynman graphs. I first start with the definition of the involved structures (vectorspace, product, unit, co-product, co-unit and antipode). A second part is devoted to the character group, whose elements map Feynman graphs to the algebra of Laurent series. Using for example dimensional regularization, Feynman rules are elements of that character group -- each n-loop Feynman graph is evaluated to a Laurent series with an n-th order pole in ε = 0. Finally, I will give some glimpses of how renormalization can be treated within this mathematical framwork. In particular, I will define two elements of the character group, which map each Feynman graph to the corresponding counterterm and `renormalized Feynman amplitude' respectively.

Mar 20 2018


Simon Plätzer
(University of Vienna)

Event Generators: The Quest for Precision

Abstract: I will give an introduction to modern particle collision event generators, which have become indispensable tools for LHC experiments and phenomenology. Focusing on the Herwig program I will outline recent development of including higher-order QCD corrections, paths to more precise parton cascade algorithms and opportunities to constrain phenomenological models.

Mar 27 - Apr 03 2018

No Lunch Seminar

Ostern - Easter Holiday

Apr 10 2018


Johanna Knapp
(University of Vienna)

The physical mathematics of string compactifications

Abstract: Calabi-Yau spaces play an important role in compactifications of string theory from ten to four dimensions. In this talk I will show how Calabi-Yaus can be constructed and analyzed by making use of a supersymmetric gauge theory in two dimensions - the gauged linear sigma model. After introducing the basic concepts, I will give a simple explicit example. If time permits, an overview of recent applications will be given.

Apr 17 2018


Marius Krumm
(IQOQI Vienna)

Two operational approaches towards causal structure and space-time in quantum mechanics

Abstract: The relation of space-time and quantum mechanics is an important ingredient for quantum gravity. The talk introduces the framework of so-called General Probabilistic Theories, which uses operational black-box scenarios described by a list of probabilities to define a large landscape of theories, including classical probability theory and quantum theory, and is supposed to describe all theories that use probabilities to predict measurement outcomes. As the formulation of this framework does not rely on a space-time structure and as this framework does not assume quantum theory, it is an ideal testing ground to investigate how quantum theory and space-time structure might constraint each other. We will present several scenarios and results for the relation of space-time and quantum theory in this framework.
Another approach towards quantum causal structure is the Process Matrix Framework by Oreshkov, Costa and Brukner. In this framework, one assumes the existence of local labs able to perform arbitrary experiments on incoming quantum systems. However, the causal relation between the labs is completely arbitrary, as long as it satisfies a minimal list of assumptions required for statistical mixtures and valid probabilities. This allows to describe the gravitational quantum switch: Here one considers the most conservative approach towards quantum gravity: Simply add superpositions of space-times to general relativity. This could be achieved via a spatial superposition of a very large mass. The induced superposition of very different time-dilations allows to create superpositions of signaling directions and could be tested via Bell inequalities for temporal order.

Apr 24 2018


Alexander Soloviev
(TU Vienna)

Semiholography for Heavy Ion Collisions

To understand the time-evolution of systems like the Quark-Gluon Plasma (QGP), it is necessary to include both weakly and strongly coupled degrees of freedom at various energy scales. Semi-holography is a non-perturbative framework that combines perturbative methods for weakly coupled partons with the holographic duality for the strongly coupled infrared in a wide range of energy scales.
I will describe a phenomenological construction aimed towards a better understanding of the QGP and present our recent findings on the collective flow near thermal equilibrium. Our results relate remarkably diverse behavior across a wide range of energy scales. Also, I will discuss the first semi-holographic simulations featuring energy exchange between a classical Yang-Mills sector and a holographic CFT.

May 1 2018

No Lunch Seminar

Tag der Arbeit - Labour Day

May 8 2018


Timon S. Gutleb
(University of Vienna)

Numerical analysis of geometric structures in simulations of the IKKT matrix model

Recently published numerical Monte-Carlo generated sample configurations of the IKKT matrix model, a potential non-perturbative approach to superstring theory, found that a (3+1) dimensional and expanding substructure emerges dynamically from the (9+1) dimensional background space. In this talk I will introduce numerical methods for the analysis of semi-classical limits of matrix- or quantum geometries and then present results of the geometry of the above-mentioned IKKT model configurations.

May 15 2018


Abhishek Chowdhury
(TU Vienna)

Negative discriminant states and where to find them

Within the framework of string theory and its low-energy limit supergravity theories, precision counting of black hole microstates has been quite successful for BPS black holes. On one side of the matching is a D-brane setup in flat space and an index calculation for BPS states and on the other end the black hole solutions in supergravity. Though the index has contributions from both negative and positive "discriminant" states, the single center black holes exists when a discriminant is +ve. This apparent discrepancy is resolved by introducing bound two-center solutions. We will try to interpret this in the context of Rademacher expansions appearing in black hole precision matching.

May 22 2018

No Lunch Seminar

Pfingsten - Pentecost

May 29 2018


Johannes Lahnsteiner
(University of Vienna)

Nonrelativistic Supergravity

Supergravity has been known for about 40 years, Newtonian gravity for over 200 years. Nevertheless, to this day nobody has constructed a supersymmetric extension of Newtonian gravity. This is remarkable, to say the least. I will present some developments in nonrelativistic geometry - so-called Newton-Cartan gravity, leading the way to Newtonian supergravity in four dimensions. In particular I will present a method to obtain the nonrelativistic limit by means of a particular dimensional reduction called null reduction. Keywords: Supergravity, Newton-Cartan gravity

Jun 5 2018


Jakob Möller
(University of Vienna)

A conjectured relation between fusion ideals

The study of Lie algebras is of utmost importance to modern day mathematical physics. Within the setting of affine Lie algebras which are an infinite dimensional extension of finite Lie algebras a conjecture about so called fusion ideals of affine Lie algebras with application in string theory has been established. In this thesis we present a proof of a special case of the conjecture, namely the case of the regular embedding of the special unitary Lie algebra su(n) in su(m) where n less or equal m are arbitrary positive integers. Furthermore we give an outlook on the case of symplectic Lie algebras.

Jun 12 2018


Felix Hummel
(TU Vienna)

Finite Temperature Coupled Cluster Methods for Extended Systems

At zero temperature coupled cluster theory is widely used to predict total energies, ground state expectation values and even excited states for molecules and extended systems. Generalizations to finite temperature exist, they are, however, very expensive since the amplitudes must be computed and stored for many Matsubara frequencies for a sufficiently accurate result. Instead of using Matsubara frequencies one can also work directly in the imaginary time domain on the compact interval [0, beta]. In this framework the transition from finite to zero temperature is uniform and comes at no extra costs for non-metallic systems.The convolutions occurring in resummed theories, such as coupled cluster, are discretized on a fitted grid, similar to the one employed by Almlöf. This reduces the number of sampling points to about a dozen, making coupled cluster calculations applicable to extended systems.

Jun 19 2018


Stephan Stetina
(TU Vienna)

Transport phenomena in the outer core of neutron stars

Multi-messenger observations of neutron stars are likely to usher in a golden age of nuclear astrophysics and promote neutron stars to one of the most precious “laboratories” in the universe. In this talk, I focus on transport phenomena in the outer core of neutron stars which impact the damping of hydrodynamic modes and r-modes, and the spin evolution of neutron stars. I discuss the microscopic physics that determine transport in a dense plasma comprised of electrons, muons, protons and neutrons, interacting via electromagnetic and strong forces. Under such conditions electrons are relativistic, degenerate, and weakly interacting and consequently play a dominant role in transport phenomena. A particular focus will be placed on dynamical screening effects, collective modes, and the role of induced electron-neutron scattering.

Jun 26 2018


Maximilian Löschner
(University of Vienna)

Lepton masses and the Multi-Higgs model

An abundance of models trying to describe the patterns in lepton masses and mixings has emerged over the past decade, many of them inspired by the rich phenomenology in the neutrino sector. Most of these models have only been studied at tree-level. In our work, we therefore try to build a generally applicable setup for studying radiative corrections to the mass and mixing preditcitons in such models in order to check their perturbative stability. All of the models referred to inherit an extended scalar sector. Therefore, we perform our studies in the Multi-Higgs Standard Model with an arbitrary number of Higgs doublets and right-handed Majorana neutrinos. After a thorough introduction into the subject, we want to present our renormalization scheme and results for one-loop lepton masses with an emphasis on gauge-dependence discussions, the treatment of tadpole contributions and the renormalization of the vacuum expectation values.

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