Vienna Theory Lunch Seminar

by Josef Leutgeb (TU), Susanne Wagner (TU), Jan Lüdtke (UV)
and Angelika Widl (UV)

Tuesdays 12:15-13:30

held alternately at:

TU Wien (TU): Wiedner Hauptstr. 8-10, yellow area, 10th floor, seminar room DB10E11

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

Idee: Idea:	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 8 2019 TU	Abhiram Kidambi (TU Wien)	Supersymmetric olympics: Wall Crossing and Jumping in gauge theory and string theory While supersymmetry is a very interesting physical theory attempting to explain many aspects of the physical universe, there are many valuable connections to mathematics too that stem from the study of supersymmetry. One problem that concerns physicists and mathematicians alike is the theory of partitions. Constructing partitions is a tremendously challenging problem due to issues that I will explain. I will go over two very important concepts that we need to keep in mind for constructing supersymmetric partition functions. The first is wall crossing phenomena which has deep connections to mathematics and the second is that of BPS jumping for which novel mathematical relations are just being discovered. No prior knowledge of supersymmetry/string theory/geometry/number theory will be assumed.
Oct 15 2019 UV	Carina Karner (TU Wien)	The role of particle shape in materials design Liquid crystals - phases of elongated molecules and colloids that exhibit orientational but no long range positional order - are the most prominent example of how phases of anisotropic particles can be be applied in materials design as Liquid crystal displays (LCDs) are used in most modern day screens. Recent advances in manufacturing colloids with well defined anisotropic shapes lead to the discovery of new ordered and partially ordered structures. This talk gives perspectives on how the properties of these new phases can be exploited for technological applications.
Oct 22 2019 TU	Olaf Krüger (Uni Wien)	From Hopf Algebras to the Renormalization Group Equation I present an algebraic derivation of the Callan-Symanzik and renormalization group equations in a given quantum field theory. This requires three basic ingredients, which I give in my talk. First, I introduce the Connes-Kreimer Hopf algebra H of Feynman graphs. Secondly, I explain the notion of renormalized Feynman rules as a linear map acting on H. In particular, certain infinite sums of graphs are mapped to the Green's functions of the theory. Finally, I motivate that these infinite sums of graphs satisfy certain fixed-point relations (so-called Dyson-Schwinger equations), which is the starting point for a beautiful derivation of the Callan-Symanzik and renormalization group equations.
Oct 29 2019 UV	Jui-Lin Kuo (HEPHY)	Astrophysical and cosmological probes of dark sector Up to now most effort in searching for new particles has focused on conventional WIMP scenarios in GeV-TeV mass range, and has not explored much the uncharted sub-GeV mass range, in which new scenarios and new production mechanism of dark matter have been proposed. In this talk, I will give an overview on astrophysical and cosmological probes of such light dark sector particles, using several examples that I have been working on for demonstration. Those results show that astrophysical and cosmological probes usually overpower terrestrial experiments in this low mass range.
Nov 5 2019 TU	Felix Hummel (TU Wien)	Matsubara frequency compression in warm dense matter In warm dense matter as found for example in gas giants, electronic correlation is comparable to the thermal fluctuations kBT. Accurately describing correlation in thermal systems poses a difficult problemfacing many obstacles. One of them is the slow convergence of the infinite sum of Matsubara frequencies. Often, hundreds or thousands of frequencies are required for reasonably converged results. Matsubara compression schemes try to approximate the infinite sum by taking a smaller set of generally non-integer Matsubara frequencies having a non-unity weight. In the spirit of a recently proposed scheme for gapped systems [Kaltak et al. arxiv:1909.01740], a scheme is proposed which can also be applied to metallic systems. A few dozen frequency points provide sufficient accuracy and the finite temperature grid converges uniformly to a zero temperature grid, allowing calculations at arbitrarily low temperatures.
Nov 12 2019 UV	Sergio Leal Gómez (Uni Wien)	TMD and spin physics The fact that QCD is non-perturbative makes tough to calculate properties of the hadrons as theirs mass, spin or even the scattering cross section. To overcome these difficulties the effective field theories can be a reliable tools. In the regimen of high energy TMD factorisation theorems give a extremely powerful framework to deal with hadronics distribution of transverse momentum, rapidity or polarisations. Through this framework we can get a better understanding of the particle polarisation inside hadrons and of hadrons themselves, improve our insight in electroweak process (e.g. gluon fusion is the main Higgs boson production process) or test possible new physics.
Nov 19 2019 TU 9th floor, seminar room DB09E23	Daniel Samitz (Uni Wien)	The Monte-Carlo Top Quark Mass The top quark, with a mass of about 173 GeV, is the heaviest particle of the standard model. The precise value of its mass is an important parameter in the context of electroweak symmetry breaking and physics beyond the standard model. Most recent measurements of the top quark mass at the LHC reach a precision of around 0.5 GeV. These measurements, based on direct reconstruction of the decay products of the top quark, rely on theoretical predictions made with Monte Carlo (MC) event generators, such that the extracted mass can not directly be understood in terms of a renormalized mass in a field-theoretically well-defined scheme, but is rather just the mass parameter of the MC generator employed. This introduces an additional uncertainty in our understanding of the top quark mass that is of the same order as current experimental uncertainties. In this talk I will discuss how the mass parameter of an angular ordered parton shower, as it is implemented in the Herwig 7 event generator, for boosted top quarks in hemisphere jet mass distributions depends on the shower cutoff and how this mass parameter can be related to well-defined mass schemes. The analytic results will be compared to the Herwig 7 event generator.
Nov 26 2019 UV	Jerzy Knopik (Uni Wien)	Asymptotic properties of the initial data for black holes in general relativity Initial data for the Einstein equations have to satisfy a set of elliptic equations called constraints. Problems arising in solving constraint equations have many surprising ties to beautiful results in Riemannian geometry. In this introductory talk I will review the basic notions and results in the theory of asymptotically flat manifolds including ADM quantities, positive mass and energy theorems and Penrose inequality. I will underline their connection with general relativity and theory of stationary black holes and sketch some open problems.
Dec 3 2019 TU	Lisa Glaser (Uni Wien)	Number + Order = Geometry Causal set theory is a pretty radical proposal to describe space-time through a partial order on elementary events. The number of events in a given region would then encode the space-time volume in that region, and the order of events is a causal order relation that encodes the topology. In this talk i will introduce causal set theory and how one can reconstruct different geometric properties from this minimal information. From there I will show some recent results about phenomenology derived from this fundamental theory, and then show how we can use computer simulations to explore the path integral over causal sets.
Dec 10 2019 UV	Sebastian Templ (HEPHY)	Looking beyond the beamspot: Searches for long-lived particles Long-lived particles (LLPs) appear in most extensions of the Standard Model (SM) in different regions of the model phase space. Searches for physics beyond the SM in decays with displaced signatures are performed in numerous experiments and aim to probe the yet-unexplored LLP phase space. This talk will present a brief overview of the field and highlight some of the experimental challenges and opportunities, focusing on the CMS experiment at the CERN-LHC.
Dec 17 2019 TU	David Erkinger (Uni Wien)	Refined swampland distance conjecture and exotic hybrid Calabi-Yaus In the first part of the talk we will introduce some concepts of string theory and the so-called swampland program. In the second part we will focus at the refined swampland distance conjecture in the Kaehler moduli space of exotic one-parameter Calabi-Yaus. We will study this conjecture with the help of the gauged linear sigma model. The latter part is based on the recently published paper arXiv:1905.05225
Dec 20 2019 -- Jan 6 2019	No Lunch Seminar	TBA
Jan 7 2019 UV	Sergio Hortner (Uni Wien)	CANCELLED , sorry for the inconvenience! Duality-symmetric worldsheet actions and the section constraint We will review the construction of duality-symmetric string worldsheet action principles, paying special attention to the Hamiltonian framework. A section condition -similar to the one arising in double field theory- needs to be imposed by hand when demanding the closure of the algebra of constraints. We shall pose the question of whether, in the particular context of the worldsheet action, the section condition can be derived as a consequence of the second-class constraints of the system.
Jan 14 2019 TU	Raphaela Wutte (TU Wien)	3d Gravity, Black Holes and Asymptotic Symmetries Studying conceptual problems in gravity is often hindered by the technical complexity of the calculations in four dimensions. Therefore, it is useful to consider toy models, such as three-dimensional gravity, that capture the relevant features while reducing technical difficulties to a minimum. In this introductory talk I will explain why 3d gravity is interesting and discuss particular solutions to Einstein's equations with negative cosmological constant. I will then introduce the concept of asymptotic symmetries and explain how they can be used to derive an infinite tower of conserved charges for spacetimes which are asymptotically negatively curved.
Jan 21 2019 UV	Christoph Roupec (TU Wien)	dS models building and the swampland The fact that our universe undergoes accelerated expansion can be explained by a de Sitter space time geometry. While simple at first sight, it has proven hard to consistently construct such solutions from string theory. Usually models are built in the low energy limit of string theory, supergravity. Still, it is non-trivial to arrive at a solution taking all requirements imposed by string theory into account. The most studied model is the so called KKLT scenario. More recently all constructions of dS vacua have come into criticism by so called swampland conjectures. In this talk I aim to give a basic overview about the topic with an emphasis on KKLT like setups and the so called dS swampland conjecture.
Jan 28 2019 UV 3rd floor, Christian-Doppler-Hörsaal	Philipp Stanzer (TU Wien)	The Quantum Null Energy Condition I will start with a reminder about (or introduction of) the classical energy conditions and talk about their purpose, applications, limitations, violations and some improvements/modifications. Given the violations, naturally the question for a new energy condition arises. The best candidate is the Quantum Null Energy Condition (QNEC) conjectured in 2015 by Bousso et al. In the second part I will introduce and discuss the QNEC and show some of our results and how we applied it to field theories via their dual gravity theory, using holography.