CPT

Calendar of Physics Talks Vienna

CONSTRAINTS ON HYPOTHETICAL INTERACTIONS FROM MEASURING THE CASIMIR FORCE
Speaker:Galina L. Klimchitskaya (Russian Academy of Sciences - Peter the Great Saint Petersburg Polytechnic University)
Abstract:We discuss the constraints on the Yukawa-type corrections to Newton's gravitational law and on the coupling constants of axion-like particles to nucleons following from recently performed experiments of Casimir physics. It is shown that the most precise measurements of the Casimir force lead to the strongest laboratory constraints on the Yukawa interaction for shorter than a few micrometers interaction range and on the axion-to-nucleon coupling in the interval of axion masses from 1 meV to a few eV. These constraints are compared with the other laboratory limits. Possible improvements due to minor modifications in the experimental setups are considered.
Date: Mon, 28.01.2019
Time: 15:00
Location:Atominstitut, Hörsaal, Stadionallee 2, Wien 2
Contact:Rene Sedmik

Tensionless strings : A perspective from the worldsheet
Speaker:Pulastya Parekh (Indian Institute of Technology Kanpur, India)
Abstract:I will be speaking about the construction of the tensionless limit of closed bosonic string theory in the covariant formulation in the light of Galilean conformal symmetry that rises as the residual gauge symmetry on the tensionless worldsheet.I will show how the analysis of the fundamental tensionless theory is related to the tensionless limit that is viewed as a contraction of worldsheet coordinates.The connection to massless higher spin states can be seen naively.This analysis can be extended to the closed superstring to obtain the Super Gallilean Conformal Algebra (SGCA),that can be realised in two distinct ways:the Homogenous and the Inhomogenous SGCA.I will also comment on the hermiticity properties of fermions in case of the Inhomogeneous tensionless superstring.We will see that the analysis of the quantum regime uncovers interesting physics.The degrees of freedom that appear ...
Date: Tue, 29.01.2019
Time: 13:45
Duration: 60 min
Location:Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:S. Fredenhagen, D. Grumiller

Thin ZrO2 films: Surface and electronic structure of insulators
Speaker:Peter Lackner (TU Wien, Institut für Angewandte Physik)
Abstract:Although the applications of zirconia (ZrO2) are manifold, its surface has not yet been studied thoroughly on an atomic level. This has a simple reason: ZrO2 is non-conductive, which makes the study of bulk zirconia with typical surface-science methods impracticable. To circumvent this issue, we searched for thin-film model systems, starting with single-monolayer films which exhibit a structure strongly dependent on the substrate below. When going to several-monolayer-thick films, deposited with home-built sputter source, surface structures influenced by the substrate are encountered up to four monolayers thickness. The best model system was found at a thickness of five monolayers. There, both the tetragonal and the monoclinic structure of ZrO2 can be prepared, and the films can be still studied with high-resolution scanning tunneling microscopy. The surface structure and electronic str
Date: Tue, 29.01.2019
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

QCD correlators at higher orders
Speaker:Matthias Jamin (ICREA Research Institut de Fisica d'Altes Energies (IFAE) Edifici Cn, Universitat Autonoma de Barcelona)
Abstract:Estimating uncertainties for perturbative predictions in QCD often hinges on our knowledge of higher-order corrections. Different approaches are available to achieve this goal like the study of scale and scheme variations, as well as investigating the general renormalon structure. Those approaches are exemplified for the case of QCD two-point correlation functions. In order to study scheme variations, it proves useful to introduce a particular scheme, the so-called C-scheme, in which the QCD beta-function is manifestly scheme invariant and known to all orders. On the other hand, the renormalon structure of QCD correlators can provide important insight into the general behaviour of their perturbative series. This general behaviour also suggests the existence of a scheme-invariant coupling in full QCD which will be introduced and its implications discussed.
Date: Tue, 29.01.2019
Time: 16:15
Duration: 60 min
Location:Fakultät für Physik, Erwin-Schrödinger-Hörsaal, Boltzmanngasse 5, 5. Stock
Contact:A. Hoang, S. Plätzer, M. Procura

High resolution tracking with scintillating fibres - The LHCb SciFi Tracker
Speaker:Dr. Lukas Gruber (CERN)
Abstract:The use of plastic scintillating fibres (SciFi) as active elements in particle detectors has a long tradition. In recent years, the development of high performance SiPM detector arrays revived the interest in the SciFi technology. Combining the two technologies allows to build intrinsically fast, low mass high resolution tracking detectors with great geometrical flexibility. As a recent example, the LHCb SciFi tracker is going to replace the current outer and inner trackers, consisting of straw tubes and silicon micro strip detectors, respectively, by using a single detector technology – 11,000 km of scintillating fibres with 250 µm diameter, enabling a spatial resolution of better than 100 µm for charged particles. The LHCb tracker requirements and environment... [full abstract available at: https://indico.smi.oeaw.ac.at/event/301/]
Date: Wed, 30.01.2019
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

Attractors of the Einstein-Klein-Gordon system
Speaker:Zoe Wyatt (Edinburgh and Vienna)
Abstract:The Milne cosmological model, a specific case of the FLRW family of cosmologies, represents an expanding universe emanating from a big bang singularity with a linear scale factor. With such a slow expansion rate, particularly compared to related isotropically expanding models (such as de Sitter), there are interesting questions one can ask about stability of this spacetime. For example previous results have shown that, when looking at the initial value problem, the Milne model is a stable solution to the vacuum Einstein, Einstein-Klein-Gordon and Einstein-Vlasov systems. Motivated by the last result, I will discuss our proof of the stability of the Milne model to the Einstein-Klein-Gordon system. This was shown recently by J. Wang using an alternative gauge and method. Thus I will also give comparisons between our method and results. This is joint work with D. Fajman.
Date: Thu, 31.01.2019
Time: 14:00
Duration: 60 min
Location:Arbeitsgruppe Gravitation, Währinger Strasse 17, Seminarraum A, 2. Stock, 1090 Wien
Contact:P.T. Chrusciel, D. Fajman

Classical de Sitter Solutions of 10d Supergravity
Speaker:Alessandro Tomasiello (University Milano-Bicocca)
Abstract:Finding de Sitter compactifications of string theory has long been a challenge. They are known to require quantum corrections, or orientifold planes, or both. Most existing models rely on effective four-dimensional actions, or work with the ten-dimensional action but involve 'smearing' the internal O-planes. After a brief review of such efforts, we present some new numerical solutions with localized and back-reacted O8-planes. While the solution is singular and strongly-coupled near one of the O8s, it exhibits the same behavior observed for such objects in flat space and in a variety of AdS solutions in various dimensions, with solid holographic cross-checks. Away from the O8s the solution can be made parametrically weakly-coupled thanks to some moduli, whose nature might however be changed by string theory corrections.
Date: Thu, 31.01.2019
Time: 16:00
Duration: 60 min
Location:Sem.R. DB gelb 10 - Freihaus, TU Wien
Contact:Timm Wrase

Cosmological Constant Problem: Deflation During Inflation
Speaker:Benjamin Koch (U. Catol. Chile, Santiago)
Abstract:We argue that the discrepancy between the Planck mass scale and the observed value of the cosmological constant can be largely attenuated, if those quantities are understood as a result of effective, and thus scale dependent, couplings. We exemplify this mechanism for the early inflationary epoch of the universe by solving the corresponding effective gap equations, subject to an energy condition. Several non-trivial checks and extensions are discussed. A comparison of our results to the renormalization group flow, obtained within the asymptotic safety program reveals a stunning agreement.
Date: Fri, 01.02.2019
Time: 16:00
Duration: 60 min
Location:Institute for Theoretical Physics, TU Wien, Seminar room 10th floor (yellow area), Wiedner Haupstr. 8-10, 1040
Contact:Anton Rebhan