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Calendar of Physics Talks Vienna
| Exploring the beginning of the universe by a nonperturbative formulation of superstring theory |
| Speaker: | Jun Nishimura (KEK) |
| Abstract: | Back in 1996, Ishibashi, Kawai, Kitazawa and Tsuchiya proposed a supersymmetric matrix model as a nonperturbative formulation of superstring theory.
The beauty of this model is that 1) there is no parameter other than one scale parameter, 2) it has the maximal supersymmetry in ten dimensions,
3) the (3+1) D space-time is expected to emerge dynamically as the eigenvalue distribution of the 10 Hermitian matrices.
I will review the status of this proposal focusing on our attempts to explore the beginning of the universe by computer simulations.
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| Date: | Tue, 15.06.2021 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | https://tuwien.zoom.us/j/95482849369?pwd=SkU2WU5hMVJBQWsyVlFXRlRvQlIvdz09 |
| Contact: | S. Fredenhagen, D. Grumiller, T. Schimannek |
| Many body methods for materials: current status and future developments |
| Speaker: | Georg Kresse (University of Vienna) |
| Abstract: | Ab initio Density functional theory has been exceedingly successful in the last four decades,however,many problems are difficult to address using local or semi-local approximations for the density functional.
This talk will summarize recent developments to go beyond density functional theory.The considered approaches are usually based on many body perturbation theory and involve two particle properties of the
many electron wave function.This allows to account for the non-locality of correlation in an elegant and accurate manner.The talk will try to discuss the underlying principles in a simple and transparent way.The methods we are currently exploring are the random phase approximation to the correlation energy for fast but often astonishingly accurate predictions[1,2,4,5]and coupled cluster methods,which are shownto yield chemical accuracy for solids, as well as "exact" solutions . . . |
| Date: | Tue, 15.06.2021 |
| Time: | 16:00 |
| Duration: | 60 min |
| Location: | https://univienna.zoom.us/j/93104933847?pwd=N0FrL0E1UHlkQWRhQTlQODVkZ3kvUT09 Meeting ID: 931 0493 3847 Passcode: 674625 |
| Contact: | A. Hoang, P. Stoffer |
| Hyperbolicity of General Relativity in Bondi-like gauges |
| Speaker: | David Hilditch (Jena) |
| Abstract: | The introduction of the Bondi-Sachs formulation was a foundational breakthrough in the understanding of gravitational waves "at" infinity, and to this day formulations of this type are routinely used in numerical relativity for a variety of purposes.
In my talk I will discuss recent work in collaboration with Thanasis Giannakopoulos and Miguel Zilhao concerning the local well-posedness of the characteristic initial boundary value problem employing such formulations.
Surprisingly, we find that these systems are only weakly hyperbolic, meaning that text-book theorems on well-posedness cannot be straightforwardly applied. Finally I will discuss the consequence of this finding in the numerical setting by using simple toy models. |
| Date: | Thu, 17.06.2021 |
| Time: | 15:00 |
| Duration: | 60 min |
| Location: | https://univienna.zoom.us/j/6540036841?pwd=SytyVkZJZzNyRG9lMm13ejlHeHRRUT09 |
| Contact: | Piotr Chrusciel, David Fajman |
| Thermalization and Hydrodynamics in 2d QFTs |
| Speaker: | Matthew Walters (Ecole Polytechnique Fédérale de Lausanne) |
| Abstract: | I will discuss the finite-temperature behavior of general 2d QFTs (obtained as relevant deformations of CFTs). At long timescales (t >> 1/T), these theories all have an effective hydrodynamic description governed by the KPZ universality class. Using KPZ universality and causality, I will derive a lower bound on the timescale characterizing the onset of this hydrodynamic behavior. The resulting bound is typically much longer than the expected quantum equilibration time of 1/T. I will also show how causality can be used to define a new thermodynamic C-function for 2d QFTs, as well as constrain the sign of the "T-Tbar" term in EFTs. |
| Date: | Thu, 17.06.2021 |
| Time: | 16:30 |
| Duration: | 60 min |
| Location: | https://tuwien.zoom.us/j/95482849369?pwd=SkU2WU5hMVJBQWsyVlFXRlRvQlIvdz09 |
| Contact: | Laura Donnay, David Andriot |
| Measuring the Thermodynamic Cost of Timekeeping |
| Speaker: | Yelena Guryanova (IQOQI Wien, ÖAW) |
| Abstract: | All clocks, in some form or another, use the evolution of nature toward higher entropy states to quantify the passage of time. Because of the statistical nature of the second law and corresponding entropy flows, fluctuations fundamentally limit the performance of any clock. This suggests a deep relation between the increase in entropy and the quality of clock ticks. Indeed, minimal models for autonomous clocks in the quantum realm revealed that a linear relation can be derived, where for a limited regime entropy linearly increases with the accuracy. Does a linear relation persist as we move toward a more classical system? We answer this in the affirmative by presenting the first experimental investigation of this thermodynamic relation in a nanoscale clock. We stochastically drive a nanometer-thick membrane and read out its displacement with a radio-frequency cavity, allowing us to ident |
| Date: | Fri, 18.06.2021 |
| Time: | 10:00 |
| Duration: | 45 min |
| Location: | on-line |
| Contact: | Marcus Huber |
| How to Calculate Differential Cross Sections at Leading Order |
| Speaker: | Angelika Widl (University of Vienna) |
| Abstract: | In this talk I give an introduction to the methods involved in calculating differential cross sections at leading order.A differential cross section with two final-state particles is easy to calculate and usually taught in introductory particle physics lectures.For a higher number of final-state particles,however,different methods have to be employed,because the calculation of the matrix element with spin sums becomes computationally expensive and the phase space integration is not possible analytically.In this talk I will present how the calculation of the matrix element is done in practice and how to perform the phase space integration using numerical Monte Carlo methods.Lastly I will put the talk in context with an ongoing project on building an NLO Monte Carlo event generator specialized for top quark productionat lepton colliders,which will use resonant-aware subtraction to deal ... |
| Date: | Fri, 18.06.2021 |
| Time: | 14:00 |
| Duration: | 60 min |
| Location: | https://univienna.zoom.us/j/93104933847?pwd=N0FrL0E1UHlkQWRhQTlQODVkZ3kvUT09 Meeting ID: 931 0493 3847 Passcode: 674625 |
| Contact: | A. Hoang, P. Stoffer |
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