Vienna Theory Lunch Seminarby Elke Aeikens (UV), Maximillian Löschner (UV), Alexander Soloviev (VUT) Tuesdays 12:1513:30
held alternately at:
We thank our kind sponsors: 
Idee: 
Wie auf vielen Universitäten praktiziert wollen wir ein LunchSeminar etablieren, das aktuelle Themen der Theoretischen Physik, die von DiplomandInnen, DoktorandInnen und PostDocs behandelt werden, aufgreift.

We want to establish a lunch seminar as practiced at other universities. The focus is on recent theoretical research done by Master students, PhDs and PostDocs.

Wie kann ich teilnehmen? 
Einfach erscheinen! Um per Email informiert zu werden, bitte in die Mailingliste eintragen. 
Just attend! To receive informations via email register for the Mailinglist. 
Mar 8 2016 
Lisa Weiß 
Simulations of a Polyoxometalate in aqueous solution Colloids represent an important part in our every day lifes ranging from food science to colours and coatings. Therefore, experimentalists developed multiple parameters and models to characterise the properties of colloids. In this work molecular dynamics simulations are used to explore the validity of these concepts for a small colloid. The influence of charge and salt content are evaluated to obtain a detailed picture how water molecules and ions arrange themselves in the surroundings of a colloid in equilibrium and non equilibrium conditions. 
Mar 15 2016 
Marissa Giustina 
SignificantLoopholeFree Test of Bell’s Theorem with Entangled Photons Local realism is the worldview in which physical properties of objects exist independently of measurement and where physical influences cannot travel faster than the speed of light. Bell’s theorem states that this worldview is incompatible with the predictions of quantum mechanics, as is expressed in Bell’s inequalities. Previous experiments convincingly supported the quantum predictions. Yet, every experiment requires assumptions that provide loopholes for a local realist explanation. Here, we report a Bell test that closes the most significant of these loopholes simultaneously. Using a welloptimized source of entangled photons, rapid setting generation, and highly efficient superconducting detectors, we observe a violation of a Bell inequality with high statistical significance. 
Mar 2229 2016 
No Lunch Seminar 
Osterferien  Easter Break 
Apr 5 2016 
Flaminia Giacomini 
Quantum mechanics with indefinite causal order In all our wellestablished theories, it is assumed that events are embedded in a global causal structure such that, for every pair of events, the causal order between them is always fixed. However, the possible interplay between quantum mechanics and general relativity may require a revision of such a paradigm, for instance when the metric tensor, and therefore the causal structure, is subject to quantum fluctuations. The process matrix framework is an operational approach to this question, and uses techniques typical of quantum information to address a problem which has been typically considered in quantum gravity. The framework retains the validity of quantum physics locally but doesn’t assume the existence of a global causal order. For example, it allows to describe causal structures corresponding to a quantum superposition of ‘A is before B’ and ‘B is before A’. The framework has been developed for both finite and infinitedimensional Hilbert spaces. The long term goal is formulating quantum fields on indefinite causal structure, as required by the highenergy regimes at which the interplay between quantum mechanics and general relativity is expected. 
Apr 12 2016 
Luis Cortés Barbado 
Hawking versus Unruh effects: What do you see when you fall into a black hole? Arguably, the most important milestone of Quantum Field Theory in curved spacetime is the discovery by Stephen Hawking that black holes should evaporate by emitting a Planckian spectrum of particles, the socalled Hawking radiation. With a similar derivation, Bill Unruh postulated that accelerated observers in empty space should perceive a thermal bath of particles with temperature proportional to their acceleration, the socalled Unruh effect. It seems clear that, for an observer following an arbitrary trajectory outside a black hole, these two effect must be present together. But, how do they combine to give the observer's net particle perception? In this talk we will address this question, within a restricted but conceptually clear framework, by using the socalled effectivetemperature function. Far from just getting a set of concrete quantitative results for different trajectories of the observer, we will obtain general results which are clearly interpretable in terms of wellknown physical phenomena. Furthermore, these results will let us to address some interesting questions: Which part of the radiation perceived can be assigned to Hawking radiation and which to the Unruh effect? Can these two effects interfere destructively? Does always the Unruh temperature scale with the proper acceleration of the observer? Is it strictly necessary to form a horizon in order to have Hawking radiation emitted? Can Hawking radiation make a test particle to float nearby a black hole due to radiation pressure? 
Apr 19 2016 
Miquel Triana 
Shock wave collisions in a family of nonconformal theories A compelling holographic model for the heavy ion collisions and the subsequent evolution of the resulting quarkgluon plasma are the shock wave collisions in AdS space. In this project we present for the first time a fully fledged shock wave collision evolution in a one parameter family of nonconformal field theories. The models studied show a nontrivial RG flow between two fixed points, and their thermodynamics resemble qualitatively (and for some magnitudes) the one of QCD. The preliminar results show how the relaxation times of the expanding plasma increase with the nonconformality, and differ very significantly from the ones computed at a linear level through the quasinormal modes spectra (wich saturate). 
Apr 26 2016 
Lukas Schneiderbauer 
Measuring finite Quantum Geometries via QuasiCoherent States A systematic approach to determine and measure numerically the geometry of generic quantum or “fuzzy” geometries realized by a set of finitedimensional hermitian matrices is developed. The method is designed to recover the semi classical limit of quantized symplectic spaces embedded in R^d including the wellknown examples of fuzzy spaces, but it applies much more generally. The central tool is provided by quasicoherent states, which are defined as ground states of Laplace or Dirac operators corresponding to localized point branes in target space. The displacement energy of these quasicoherent states is used to extract the local dimension and tangent space of the semiclassical geometry, and provides a measure for the quality and selfconsistency of the semiclassical approximation. 
May 3 2016 
Alexander Komech 
On Bohr's transitions to quantum stationary states The uptodate mathematical structure of Quantum Theory is a mixture of dynamical (Schrödinger, Klein  Gordon, Dirac, Yang  Mills, Maxwell, ...) PDEs with Quantum Postulates (Bohr's transitions between stationary orbits, de Broglie's waveparticle duality, Born's probabilistic interpretation, ...). Our ultimate goal is to discover these postulates as inherent properties of dynamical equations. This is a twofold problem: first, we should find the corresponding mathematical formulation of a postulate, and afterwords, justify it in a suitable framework. We suggest to treat i) the Bohr's transitions as a global longtime attraction to solitary waves, and ii) the waveparticle duality as a global longtime attraction to solitons. 
May 10 2016 
Moritz Preisser 
The top quark mass: Calibrating PYTHIA's top quark mass parameter using massive event shapes Abstract: The top quark is the heaviest particle in the Standard Model (SM) of particle physics. For a variety of reasons it is very important to know its mass with high precision. In this talk I am going to review a class of precise top quark mass determinations and their relation with General Purpose Monte Carlo event generators (GPMCs) such as PYTHIA. After that I will present a method for extracting a theoretically well defined top quark mass value from such determinations using Effective Field Theory (EFT) methods. In the end I am going to show recent results and an outlook on future work. 
May 17 2016 
No Lunch Club 
Pfingsten  Pentecost 
May 24 2016 
Silvano Ferrari 
Selfassembly of inversepatchy colloids into Manner Schnitten Inversepatchy colloids (IPC) are heterogeneously charged; two small sites (the socalled patches) carry charge of the opposite sign of the rest of the surface. The interplay between the regions of likeunlike charge gives rise to quite a few unusual lattices; among them, we studied a very peculiar structure where liquid regions are trapped between solid planar layers, like the melted chocolate is trapped between wafer layers in a Manner Schnitten in a hot summer day. Using molecular dynamics, we determined the stability of this structure with respect to the model parameters (charge and patch amplitude). 
May 31 2016 
Cancelled 

Jun 7 2016 
Dr. Miguel Verdugo 
On the origin and life of cluster galaxies Clusters of galaxies are the most massive objects in the Universe. As such they sit at the crossroads between cosmology and astrophysics, allowing the investigation of a variety of phenomena. Clusters of galaxies also feature a different galaxy population in comparison to their surroundings, with galaxies in the field being mostly starforming whereas galaxies in clusters are mostly passive. This dichotomy has baffled astronomers for years and no model currently predicts all the observed features. In this talk I will concentrate in the possible origins of this population and the efforts being done in Vienna to make progress in some long standing questions. I will also introduce aspects of structure formation and galaxy evolution which are relevant for the topic of this talk. 
Jun 14 2016 
Dr. Johannes Lachner 
Accelerator Mass Spectrometry at VERA Accelerator Mass Spectrometry (AMS) is a powerful experimental technique to determine trace amounts of nuclides in environmental or artificial samples. This finds many applications, e.g. in nuclear astrophysics, geology, or oceanography. The setup in Vienna (VERA: Vienna Environmental Research Accelerator) is now in use since 20 years and can be used to measure many longlived nuclides such as 10Be, 14C, 36Cl, 129I or U and Pu isotopes. The key parameters for a successful AMS measurement are the efficient counting of the ions of interest and the effective suppression of potential background arising from molecular and atomic isobars or from neighbouring abundant isotopes. I will present recent technical developments towards our aim to suppress isobaric background in an interaction of the beam particles with a LASER and show some exemplary applications of radionuclides in other sciences. 
Jun 21 2016 
Alexander Haber 
Flux Tubes Interacting with Superfluids In compact stars, nucleons form an interacting multifluid system of a neutron superfluid and a proton superconductor. The rotation of the star and the strong background magnetic fields generate superfluid vortices and superconducting flux tubes in the core. After a phenomenological introduction to superconductivity, I will review how these phenomena can be described in the context of quantum field theory. Using a microscopic fieldtheoretical model of two coupled bosonic fields with entrainment and density coupling, the phase structure of the multifluid system is examined. In particular, the superconducting typeI/typeII transition and multiflux quantum phases under the influence of the neutron condensate are investigated, including an effective interaction between the flux tubes. 
Jun 28 2016 
Tin Ribic 
The FalicovKimball model  Dynamical Mean Field Theory and beyond A lot of todays most intriguing effects in material science are observed in systems with strongly correlated electrons. Unfortunately, interacting quantum systems are computationally very expensive to treat. The FalicovKimball model is a rare example of a nontrivial, interacting quantum system, for which some analytical results can be obtained. Results on local corellators of mobile electrons in the FalicovKimball model within the framework of dynamical mean field theory will be discussed. These are then used as building blocks for reincluding nonlocal correlations into the model via expansion schemes. Since analytical expressions for the local correlators are available, many calculations which would usually need to be treated computationally can be performed by hand. This allows investigation of a simple, interacting quantum system on one hand, but simultanously provides a benchmark for the behaviour of methods developed for treatment of more general interacting systems. 
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