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Calendar of Physics Talks Vienna
| 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 |
| 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 |
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