CPT

Calendar of Physics Talks Vienna

A proof of the constancy of surface gravity for non-degenerate compact horizons
Speaker:Ettore Minguzzi (Firenze)
Abstract:Smooth compact totally geodesic null hypersurfaces (horizons) arise naturally as Cauchy horizons for partial Cauchy hypersurfaces. Here I outline a recent proof that if they admit an incomplete generator (non-degenerate) then the surface gravity can be normalized to a non-zero constant. The proof is, in its most technical part, independent of the approach of Isenberg-Moncrief and Bustamante-Reiris. Also the result holds just under the dominant energy condition, i.e. no vacuum assumption is required. If time permits, I shall also outline the proof that they are actually Cauchy horizons bounded on one-side by a region of chronology violation. (This is joint work with Sebastian Gurriaran, ENS Paris-Saclay)
Date: Thu, 28.10.2021
Time: 14:00
Duration: 60 min
Location:ZOOM https://univienna.zoom.us/j/6540036841?pwd=SytyVkZJZzNyRG9lMm13ejlHeHRRUT09
Contact:Piotr Chrusciel, David Fajman

Black-Hole Scattering, Eikonal Exponentiation and Gravitational Waves
Speaker:Carlo Heissenberg (Nordita & Uppsala)
Abstract:The eikonal exponentiation of gravity amplitudes is a non-perturbative resummation whereby certain high-energy divergent terms, which would naively violate unitarity bounds, combine into a harmless phase factor. Eikonal techniques also offer a natural strategy to calculate classical gravitational observables directly from the loop-expansion of scattering amplitudes. In this talk, I will discuss how the eikonal can be applied to obtain the deflection angle for the collision of two non-spinning black holes with generic center-of-mass energies, up to order O(G^3). This calculation captures both conservative and dissipative “radiation-reaction” effects, and yields a deflection angle with a smooth behavior at high energies, where it agrees with the universal massless result. [...]
Date: Thu, 28.10.2021
Time: 16:30
Duration: 60 min
Location:Seminar room, 10th floor, Yellow building
Contact:Laura Donnay

Efficient nano-scale single photon antennas based on dark states in quantum emitter rings
Speaker:Helmut Ritsch (Universität Innsbruck)
Abstract:Studying the optical absorption and emission properties of nanoscopic quantum emitter structures we found unique properties of subwavelength rings. As particular striking example we identify a sub-wavelength sized ring of exactly 9 identical dipoles with an extra identical emitter with a extra loss channel at the center as the most efficient configuration to deposit incoming photon energy to center without reemission. The enhancement is most pronounced a given resonance frequency but still stays visible for broadband light absorption. For very tiny structures below a tenth of a wavelength a full quantum description exhibits an even larger enhancement than predicted from a classical dipole approximation. The origin of the effect can be tied to a specific geometric property of nonagons allowing for the appearance of a special collective dark state with dominant center occupation. By specia
Date: Fri, 29.10.2021
Time: 10:00
Duration: 45 min
Location:Atominstitut, Hörsaal and hybrid form
Contact:Peter Rabl

Is the Chiral Magnetic Effect fast enough?
Speaker:Karl Landsteiner (Univ. Autonoma Madrid)
Abstract:It depends! The Chiral Magnetic Effect (CME) is the generation of an electric current in a magnetic field due to a chirality imbalance. It is supposed to occur in non-central heavy ion collisions. We develop a holographic model to address the question how fast the CME builds up in an out-of-equilibrium setup. Our findings indicate that there is a significant time delay. In the context of heavy ion collisions with a short lifetime of the magnetic field the model leads to the conclusion that the CME is not fast enough at the LHC but might well be observable at RHIC. Along the the way I will also try to briefly review the experimental efforts to measure CME and especially highlight the recent results from the isobar run at RHIC.
Date: Fri, 29.10.2021
Time: 14:00
Duration: 60 min
Location:Hybrid: TU Wien, conference room 9th floor (green), Wiedner Haupstr. 8-10 and https://tuwien.zoom.us/j/91735458787?pwd=cjBqK3ZCWHRZaFJXSS82dXFvWVNLZz09
Contact:Anton Rebhan (TU Wien)