
Vienna Theory Lunch Seminarby Florian Ecker (TU), Christopher Lieberum (UV), Florian Lindenbauer (TU) and Maximilian Ofner (UV) Tuesdays 12:3013:45held alternately
at:
We thank our kind sponsors:

Idee: 
Nach pandemiebedingter Pause wollen wir das Vienna theory lunch
seminar wiedererwecken, das aktuelle Themen der Theoretischen
Physik, die von DiplomandInnen, DoktorandInnen und PostDocs
behandelt werden, aufgreift. 
After a break due to the pandemic we want to revive the Vienna
theory lunch seminar. 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. 
Mar 5 2024 UV 
Tim Lüders 
The functorial axiomatization of topological quantum field theory In this talk, I will give a lightning introduction to topological quantum field theory in its functorial axiomatization, due to Atiyah and Segal. We start by exploring the very basics of the mathematical discipline of category theory, which will then be used as a convenient tool to package essential properties of Feynman’s path integral into a mathematically rigorous framework. Examples of physical theories that can be described in this setting include ChernSimons theory as well as topological sigma and state sum models. I will finish the talk by mentioning several natural generalizations of the introduced mathematical structures, and what physical interest each of them carries. 
Mar 12 2024 
Rektorstag Uni Wien 


Mar 19 2024 
Mario Hudelist 
Spacetime curvatureinduced corrections to Rytov's law in optical fibers According to Rytov's law, the polarization vector of light follows a FermiWalker transport equation in optical fibers. Recent advancements in theory propose a modification to Rytov's law due to fiber bending. The aim of this talk is to further extend these predictions from flat to curved spacetime. This involves perturbatively solving Maxwell's equations under the assumption that the wavelength is significantly shorter than the fiber radius, as well as the characteristic lengthscales of the ambient spacetime. This results in a coupling of the polarization vector to the Riemann curvature tensor. 
Mar 26 2024 
Easter break 
 
Apr 02 2024 
Easter break 
 
Apr 09 2024 UV 
Andreas Schmitt 
Superconducting baryon crystal at strong magnetic field Strongly interacting matter in extreme magnetic fields occurs in heavyion collisions and neutron stars and is of theoretical interest for the phase structure of Quantum Chromodynamics. It was previously found that a socalled Chiral Soliton Lattice is formed at sufficiently large magnetic fields and baryon chemical potentials. Using chiral perturbation theory and methods from ordinary typeII superconductivity I will discuss the instability of the Chiral Soliton Lattice and the resulting transition to a 3D crystalline structure. This structure is an inhomogeneous condensate of neutral and charged pions and thus a superconductor with spatially modulated magnetic field and, due to the axial anomaly, spatially modulated baryon number. I will also speculate what this new phase implies for the QCD phase structure. 
Apr 16 2024 TU 
Paul Hotzy 
Towards the computation of realtime observables in YangMills theories on the lattice Lattice Quantum Chromodynamics (LQCD) is one of the most successful methods for making nonperturbative predictions in highenergy physics. Despite its achievements, traditional computational techniques encounter limitations — arising from the notorious sign problem — when dealing with dynamic observables in physical time or at nonvanishing chemical potential. Our recent work focuses on the complex Langevin (CL) method, which aims to circumvent these challenges by generalizing the Stochastic Quantization approach. We have significantly improved and successfully applied CL to realtime SU(N) gauge theories on a 1+3 dimensional lattice for the first time. In this talk, I present our recent advances in calculating unequaltime correlation functions directly from first principles. These developments may lay the cornerstone for future applications of CL, enabling the computation of spectral functions and transport coefficients. These quantities are of high phenomenological interest in strongly interacting systems such as the Quark Gluon Plasma (QGP). 
Apr 23 2024 UV 
Argam Ohanyan 
Recent developments in nonsmooth spacetime geometry In Einstein's theory of General Relativity, nonsmooth phenomena naturally arise, e.g. in questions regarding the extendibility of spacetimes, geodesic singularities, or cosmic censorship. Recently, a new approach to spacetime geometry has gained significant popularity, i.e. the theory of Lorentzian length spaces. It is a new way to describe nonsmooth spacetimes, and is very promising to deliver great insights, given the success of similar approaches in positive definite geometry (Alexandrov spaces, metric measure geometry, etc.). In this talk, we will introduce some of the basic notions in this theory and discuss recent progress. 
Apr 30 2024 TU 
David Globosits 
A Photonic Floquet Scattering Matrix for WavefrontShaping in TimePeriodic Media The physics of waves in timevarying media provides numerous opportunities for wave control that are unattainable with static media. In particular, Floquet systems with a periodic time modulation are currently of considerable interest. In my talk, I will demonstrate how the scattering properties of a finite Floquet medium can be correctly described by a static Floquet scattering matrix, which satisfies a pseudounitary relation. Using this Floquet scattering matrix, I will further show how one can identify light pulses that are optimally shaped both in their spatial and temporal degrees of freedom for the optical micromanipulation of timevarying media. 
May 07 2024 TU 
Marius Oancea 
Gravitational memory effects for particles and wave packets Gravitational waves can generally influence the dynamics of test objects with which they interact. Changes in the relative dynamics of test objects can persist even after the gravitational wave has passed and spacetime is again flat. These are generally referred to as gravitational memory effects, since the properties of the passing gravitational wave remain encoded in the relative dynamics of test objects. In this talk, I will discuss gravitational memory effects in plane wave spacetimes for different classes of test objects: particles following geodesics, spinning particles with nongeodesic motion, and test scalar fields. For all these objects, memory effects are encoded into a set of four memory tensors that depend on the gravitational wave profile. Joint work with Abraham Harte, Thomas Mieling, and Florian Steininger. 
May 14 2024 TU 
Markus Leuthner 
Longitudinal structure of relativistic heavyion collisions from the (3+1)D dilute Glasma The (3+1)D dilute Glasma is a novel framework for the computation of rapiditydependent earlytime observables in relativistic heavyion collisions. First, I discuss the QCD phase diagram and the extremely successful class of experiments called heavyion collisions performed at RHIC and LHC. I then show how the Glasma, the first stage after a collision of relativistic nuclei, emerges in the Color Glass Condensate effective theory for high energy QCD. The dynamics of the Glasma are governed by the classical YangMills equations, which I will solve for longitudinally extended sources, employing the dilute approximation. I obtain an analytic expression for the energymomentum tensor of the Glasma as a function of rapidity. This opens up new insights into the longitudinal dynamics of the Glasma, which have previously been notoriously hard to simulate. Finally, I will show some numerical results for earlytime observables in relativistic heavyion collisions obtained in the dilute Glasma framework. 
May 21 2024  
Pentecost 


May 28 2024 UV 
Iva Lovrekovic 
Asymptotic symmetries of new 3d conformal higher spin theories for low spins We study asymptotic symmetries for 3d ChernSimons theory as a gauge theory of so(3,2), sl_4 and sl_5 algebras. For the near horizon boundary conditions we present solutions from several projectors from ChernSimons to the metric formulation. We also study the classification according to so(3,2) one parameter subgroups and classify obtained solutions. 
Jun 04 2024 TU 
Tanmay Biswas 
Phase separation dynamics in a binary mixtures of ultrasoft particles Phase separation plays a crucial role in determining the selfassembly of biological and soft matter systems. In the former case, liquidliquid phase separation inside a cell leads to the formation of various macromolecular aggregates. The interaction among these aggregates is soft and the particles are generally modelled by ultrasoft particles. We have studied the phase separation dynamics of binary mixture of ultrasoft particles (with species A and B). When quenched to a lower temperature below critical temperature, the system undergoes a phase separation into an Aand a Brich phase. In detailed and extensive molecular dynamics simulations we have identified the critical point. When cooling the system the domains of the two components grow in a powerlaw manner with an exponent α = 1/3) which is consistent with the LifshitzSlyozov law. In a subsequent step we have exposed the system – as it is cooled down to low temperatures  to shear and have studied the stress response of the system to the these external forces; in their presence the domains grow with exponents α = 4/3 and α = 1/3 in the shear and the gradient direction, respectively. In particular we have analysed how spatial inhomogeneities (which are characteristic for the phase separation scenario) evolve under the shear forces. 
Jun 11 2024 UV 
Matthias Ostermann 
CANCELLED: Unfortunately, the take has to be cancelled. Sorry for the inconvenience! Stable blowup for wave maps and YangMills models The wave maps equation first appeared in particle physics as a nonlinear sigma model and the YangMills equations originated from gauge theory for the strong interaction. They constitute prototypes of nonlinear geometric wave equations which, remarkably, have an explicit solution that forms a singularity in finite time. To determine the significance of these blowup solutions for the underlying dynamics, one studies their stability. In this talk, we give an elementary introduction to the mathematical analysis of blowup in both model equations and present some new stability results. 
Jun 18 2024 TU 
Simon Panyella Pedersen 
Analysing the optical nonlinearity of a cavitylike subwavelength atomic array Subwavelength arrays of quantum emitters offer an interesting approach to coherent lightmatter interfacing, using ultracold atoms or twodimensional solidstate quantum materials. The combination of collectively suppressed photonlosses and emerging optical nonlinearities due to strong photoncoupling to mesoscopic numbers of emitters holds promise for generating nonclassical light and engineering effective interactions between freely propagating photons. In my talk I will describe the interaction between photons and a specific configuration of twolevel atoms, namely two parallel 2D arrays individually acting like mirrors and together forming a cavitylike system. The long confinement of photons in this system results in an accumulation of correlation between the photons, revealing their strong effective interaction mediated by the atoms. While most studies have thus far relied on numerical simulations, I will furthermore describe a Green's function approach that permits analytical investigations of the nonlinear processes of the system. The approach yields intuitive insights into the nonlinear response of the system and offers a promising framework for a systematic development of a manybody theory for interacting photons and manybody effects on collective radiance in twodimensional arrays of quantum emitters. 
Jun 25 2024 TU 
Sukrut Mondkar 
Learning holographic horizons We apply machine learning to understand fundamental aspects of holo graphic duality, specifically the entropies obtained from the apparent and event horizon areas. We show that simple features of only the time series of the pressure anisotropy can predict the areas of the apparent and event horizons in the dual bulk geometry at all times. Given that simple Vaidyatype metrics constructed just from the apparent and event horizon areas can be used to approximately obtain unequal time correlation functions, we argue that the corresponding entropy functions are the measures of information that need to be extracted from simple onepoint functions to reconstruct specific aspects of correlation functions of the dual state with the best possible approximations. 
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