Calendar of Physics Talks Vienna

The infrared physics of bad theories
Speaker:Stefano Cremonesi (Kings College London)
Abstract:Three-dimensional gauge theories with eight supercharges (3d N=4) have a rich moduli space of supersymmetric vacua with different low energy physics. This infrared physics is well understood for theories with large enough number of flavours ("good theories"), but less so if the number of flavours is small ("bad theories"). In this talk I will focus on 3d N=4 super-QCD theories with U(N) gauge group and N_f flavours of fundamental hypermultiplets. After reviewing known results and puzzles about such theories, I will discuss their quantum corrected moduli space of vacua, which consists of Higgs, Coulomb and mixed branches, and their low energy physics as N and N_f are varied. As a by-product, I will clarify if and in which sense bad U(N) gauge theories with N_f >= N flavours flow to their "Seiberg dual" good U(N_f-N) theories with N_f flavours (plus free fields) at low energies, as . . .
Date: Mon, 24.04.2017
Time: 14:15
Duration: 60 min
Location:Fakultät für Physik, Kleiner Seminarraum, Boltzmanngasse 5, 5. Stock
Contact:S. Fredenhagen, H. Steinacker

Electron trapping in nanocrystalline titanium dioxide
Speaker:Keith McKenna (University of York, UK)
Abstract:The trapping and mobility of electrons in nanocrystalline oxide materials underpins a diverse range of applications in areas such as solar energy generation, catalysis, gas sensing and nanoelectronics. However, directing probing the properties of electrons in such complex nanocrystalline systems is extremely challenging. Here, we provide insight into these important issues through first principles based modeling of the interaction of electrons with surfaces and grain boundaries in rutile TiO2. We show that different surface orientations exhibit markedly different electron affinities: some preferring to trap electrons with others repelling electrons. The equilibrium nanocrystal morphology exposes both electron trapping and electron repelling facets and therefore is predicted to posses highly anisotropic electron trapping properties [1]. Interfaces between nanoparticles (grain boundaries)
Date: Tue, 25.04.2017
Time: 16:00
Location:Technische Universität Wien, Institut für Angewandte Physik, E134 yellow tower „B“, 5th floor, Sem.R. DB gelb 05 B (room number DB05L03), 1040 Wien, Wiedner Hauptstraße 8-10
Contact:Univ.Prof. Dr. Ulrike Diebold

The GENEVA Monte Carlo framework: improving SMC with resummation
Speaker:Simone Alioli (CERN)
Abstract:I will discuss the GENEVA Monte Carlo framework, as an example of how to include analytic resummation in Shower Monte Carlo event generators. GENEVA combines the fully-differential NNLO calculation with higher-order resummation of the resolution parameter, providing a systematic assessment of perturbative uncertainties. The resulting parton-level events are further combined with parton showering and hadronization in Pythia 8. For the Drell-Yan case presented, the 0-jettiness resummation is carried out to NNLL', which consistently incorporates all singular virtual and real NLO corrections. In this way, the perturbative accuracy of 0-jet-like resummation variables is significantly improved beyond the parton shower approximation. I will show comparisons with LHC measurements at 7 TeV from ATLAS, CMS and LHCb, including results for several underlying-event sensitive observables.
Date: Tue, 25.04.2017
Time: 16:15
Duration: 60 min
Location:Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:A. Hoang, H. Neufeld

The gravitational field of a laser pulse
Speaker:Dennis Raetzel (Vienna)
Abstract:As Einstein's equations tell us that all energy is a source of gravity, light must gravitate. However, because changes of the gravitational field propagate with the speed of light, the gravitational effect of light differs significantly from that of massive objects. In particular, the gravitational force induced by a laser pulse is due only to its creation and annihilation and decays with the inverse of the distance to the pulse. We can expect the gravitational field of light to be extremely weak. However, the properties of light are premises in the foundations of modern physics: they were used to derive special and general relativity and are the basis of the concept of time and causality in many alternative models. Studying the back-reaction of light on the gravitational field could give new fundamental insights to our understanding of space and time as well as classical and . . .
Date: Thu, 27.04.2017
Time: 14:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Raum 218, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel

Mathieu Moonshine and Symmetry Surfing
Speaker:Christoph Keller (ETH Zurich)
Abstract:I will give a brief introduction to moonshine, the surprising connection between modular forms and sporadic simple groups. I will quickly discuss the original monstrous moonshine, and then talk about the more recently discovered Mathieu moonshine. I will explain why the explanation of the original moonshine most likely does not work for this new type of moonshine. I will then discuss a proposed explanation due to Taormina and Wendland, namely the idea of `symmetry surfing', i.e. combining the symmetries of different K3 sigma models. I will present some new results which provide evidence that symmetry surfing should work also for all higher BPS states. This is based on work with Matthias Gaberdiel and Hynek Paul.
Date: Thu, 27.04.2017
Time: 16:00
Duration: 60 min
Location:SEM 136, TU Wien, Freihaus, 10th floor (Wiedner Hauptstr. 8-10, A-1040 Vienna)
Contact:Timm Wrase