CPT

Calendar of Physics Talks Vienna

"Precision searches for new physics using optically levitated sensors"
Speaker:David Moore ((CoQuS Talk))
Abstract:for further information please visit: https://coqus.at/study-program/colloquium/
Date: Mon, 14.10.2019
Time: 16:30
Duration: 120 min
Location:Lise Meitner Lecture Hall, Strudlhofgasse 4, 1st floor, 1090 Vienna
Contact:CoQuS Team

Lifting BPS States on K3 and Mathieu Moonshine
Speaker:Ida Zadeh (ICTP, Triest)
Abstract:Joint TU / UV Theory Seminar: The elliptic genus of K3 is an index for the 1/4-BPS states of its sigma-model. At the torus orbifold point there is an accidental degeneracy of such states. We blow up the orbifold fixed points and show that this fully lifts the accidental degeneracy of the 1/4-BPS states with dimension h=1. Thus, at a generic point near the Kummer surface the elliptic genus measures not just their index, but counts the actual number of these BPS states. Finally, we comment on the implication of this for symmetry surfing and Mathieu moonshine.
Date: Tue, 15.10.2019
Time: 13:45
Duration: 60 min
Location:Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:S. Fredenhagen, D. Grumiller. C. Zwikel, T. Schimannek

Higher-spin generalisations of gravity
Speaker:Stefan Fredenhagen (Univ. Wien)
Abstract:Im Rahmen des Teilchenphysikseminars: There are many different approaches to quantum gravity. One of the most prominent candidates is string theory: it offers a perturbative description of quantum gravity, and can unify the interactions at least in principle. In an extreme stringy limit in which the string length becomes large, one expects string theory to be described by theories containing higher-spin gauge fields. Such theories are of interest independent of the relation to string theory, and they provide fascinating higher-spin generalisations of gravity. I review different approaches towards formulating higher-spin gauge theories and discuss recent results in the Fronsdal-Noether program.
Date: Tue, 15.10.2019
Time: 16:15
Duration: 60 min
Location:Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:A. Hoang, S. Plätzer

Fishing in a sea of Xe: Hunting for Majorana neutrinos with nEXO
Speaker:Dr. Thomas Brunner (Physics Department, McGill University, Montréal, QC, Canada and TRIUMF, Vancouver, BC, Canada)
Abstract:Despite tremendous progress in understanding the fundamental properties of neutrinos over the past decades, several key questions remain unanswered. In particular, we do not yet know if neutrinos are Majorana particles (i.e., are neutrinos and antineutrinos identical?). The most sensitive experimental probe of the Majorana nature of the neutrino is to search for the lepton-number violating neutrinoless double-beta decay (0νββ). A positive observation of this decay mode would confirm that neutrinos are Majorona particles and demonstrate physics that is not explained by the Standard Model. The EXO-200 collaboration is currently searching for 0νββ decays in 136Xe in a detector containing ~175kg of enriched liquid Xe, and has provided one of the most sensitive limits on the half-life of this decay (T1/2>3.5 x 1025 yr at 90% C.L.) ... [full abstract: https://indico.smi.oeaw.ac.at/event/349/]
Date: Tue, 15.10.2019
Time: 17:00
Duration: 60 min
Location:Stefan-Meyer-Institut, Boltzmanngasse 3, 1090 Wien, Seminarraum 3-2-08 (2. Stock)
Contact:Prof. Dr. Eberhard Widmann, Dr. Martin Simon

Position and momentum mapping of phonons & electronic excitations in monolayers and graphene nanostructures
Speaker:Thomas Pichler (Faculty of Physics, University of Vienna)
Abstract:Recent advances in improving the energy resolution in electron energy loss spectroscopy inside a transmission electron microscope enables the application in different energy scales ranging from the direct measurements of site selective core level spectroscopy, truly local and momentum resolved valence band excitations down to the energy of phonon spectroscopy. Here I ll present our new results on graphene nanostructures combining high-resolution EELS with high-resolution TEM. Regarding core level excitations well separated peaks are obtained from a single freestanding nanotube with the local chiral index and unambiguously related to the van Hove singularities. The local EELS response directly determines the defect modulated gap transition in semiconducting nanotubes and correlates it to the optical conductivity. This allows for the first time to unravel the influence of an identified …
Date: Wed, 16.10.2019
Time: 14:15
Location:Seminar room FH gelb 10, Institute for Theoretical Physics – Vienna University of Technology, Wiedner Hauptstraße 8 – 10, 10th floor, B (yellow tower)
Contact:Joachim Burgdörfer

Global existence of Dirac-wave maps with curvature term on expanding spacetimes
Speaker:Volker Branding (Univ. Wien)
Abstract:The action functional of the supersymmetric nonlinear sigma model is an importantmodel in modern quantum field theory.From a mathematical point of view it consists of a map between two manifolds and a vector spinor defined along that map.If one chooses a Riemannian domain manifold its critical points couple the elliptic harmonic map equation with the vector spinor,this system became known as Dirac-harmonic maps and variants thereof.Since the action functional of the supersymmetric nonlinear sigma model is unbounded from below it is very difficult to obtain existence results for this system.However,in the case of a globally hyperbolic domain manifold the critical points lead to the Dirac-wave map system which is a hyperbolic system of partial differential equations.In this setup unbounded action functionals are much better to deal with.We will present an existence result for wave maps ..
Date: Thu, 17.10.2019
Time: 14:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Raum 218, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel, D. Fajman

Extremal surfaces, de Sitter entropy and entanglement in ghost theories
Speaker:Narayan Krishnan (Chennai Mathematical Institute)
Abstract:We describe connected timelike codim-2 extremal surfaces stretching between the future and past boundaries in the static coordinatization of de Sitter space. These are analogous to rotated versions of certain surfaces in the AdS black hole. The existence of these surfaces via the dS/CFT framework suggests the speculation that dS4 is dual to two copies of ghost-like CFTs in a thermofield-double-type entangled state. In studies of entanglement in ghost theories and "ghost-spin" chains, we show that similar entangled states in two copies of ghost-spin ensembles always have positive norm and positive entanglement.
Date: Thu, 17.10.2019
Time: 16:00
Duration: 60 min
Location:TU Wien, Wiedner Hauptstraße 10, Yellow Area, Seminar Room
Contact:D. Grumiller, C. Zwikel