Vienna Theory Lunch Seminar by Josef Leutgeb (TU), Susanne Wagner (TU), Jan Lüdtke (UV) Tuesdays 12:1513:30
held alternately at:
We thank our kind sponsors: 
Idee: 
Wie auf vielen Universitäten praktiziert wollen wir ein LunchSeminar etablieren, das aktuelle Themen der Theoretischen Physik, die von DiplomandInnen, DoktorandInnen und PostDocs behandelt werden, aufgreift.

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.

Wie kann ich teilnehmen? 
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 
Abhiram Kidambi 
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 
Carina Karner 
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 
Olaf Krüger 
From Hopf Algebras to the Renormalization Group Equation I present an algebraic derivation of the CallanSymanzik 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 ConnesKreimer 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 fixedpoint relations (socalled DysonSchwinger equations), which is the starting point for a beautiful derivation of the CallanSymanzik and renormalization group equations. 
Oct 29 2019 
JuiLin Kuo 
Astrophysical and cosmological probes of dark sector Up to now most effort in searching for new particles has focused on conventional WIMP scenarios in GeVTeV mass range, and has not explored much the uncharted subGeV 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 
Felix Hummel 
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 noninteger Matsubara frequencies having a nonunity 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 
Sergio Leal Gómez 
TMD and spin physics The fact that QCD is nonperturbative 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 
Daniel Samitz 
The MonteCarlo 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 fieldtheoretically welldefined 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 welldefined mass schemes. The analytic results will be compared to the Herwig 7 event generator. 
Nov 26 2019 
Jerzy Knopik 
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 
Lisa Glaser 
Number + Order = Geometry Causal set theory is a pretty radical proposal to describe spacetime through a partial order on elementary events. The number of events in a given region would then encode the spacetime volume in that region, and the order of events is a causal order relation that encodes the topology.

Dec 10 2019 
Sebastian Templ 
Looking beyond the beamspot: Searches for longlived particles Longlived 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 yetunexplored 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 CERNLHC. 
Dec 17 2019 
David Erkinger 
Refined swampland distance conjecture and exotic hybrid CalabiYaus In the first part of the talk we will introduce some concepts of string theory and the socalled swampland program. In the second part we will focus at the refined swampland distance conjecture in the Kaehler moduli space of exotic oneparameter CalabiYaus. 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 
Sergio Hortner 
CANCELLED
, sorry for the inconvenience! We will review the construction of dualitysymmetric 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 secondclass constraints of the system. 
Jan 14 2019 
Raphaela Wutte 
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 threedimensional 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 
Christoph Roupec 
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 nontrivial to arrive at a solution taking all requirements imposed by string theory into account. The most studied model is the so called KKLT scenario.

Jan 28 2019 
Philipp Stanzer 
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. 
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