Vienna Theory Lunch Seminarby Christian Ecker (VUT), Alexander Haber (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 10 2015 
Pascal Anastasopoulos 
String Phenomenology Abstract: Dbrane realizations of the Standard Model predict new particles and couplings. In this seminar we will focus on a) anomalous Z's gauge bosons and b) excited states for each matter field of the SM. If the string scale is low (at a few TeV range), such particles can be visible at the LHC. 
Mar 17 2015 
Kyrylo Simonov 
Is quantum linear superposition exact on all energy scales? A unique case study with flavour oscillating systems Abstract: Quantum mechanics, in its standard formulation, gives an extremely accurate description of microscopic systems and, up to date, no experiment has found any contradictions to its predictions. However, the quantum theory meets some conceptual difficulties with macroscopic systems: the principle of linear superposition, which is a corner stone of quantum theory, conflicts our everyday experience: Why for instance, a table or cat is never found to be in two places at the same time? And how does a measurement process break the superposition of microscopic systems? Models of spontaneous collapses, so called collapse models, provide a powerful, mathematical complete approach to preserve quantum linearity at the microscopic level while breaking it on the macroscopic level and giving new predictions in the region inbetween. This is achieved by modelling the reduction of the wave function as a physical process. A highly attractive property of such models is that they can be excluded experimentally e.g. via modern ongoing matter wave interferometry or via under ground Xray experiments. This talk gives an introduction to collapse models and the idea behind. Then it outlines how neutral flavour oscillating Kmesons, being superpositions of two different masseigenstates, can uniquely contribute to the testing of collapse models. 
Mar 24 2015 
Vicent Mateu 
Recent progress in massless and massive event shapes Abstract: In this talk I will give an overview of our recent developments in the theoretical description of the event shapes, and will discuss the results obtained in recent analyses for the determination of the strong coupling constant. In the massless case I will focus on thrust and Cparameter, showing results for resummation at N3LL order plus threeloop matrix elements, and the analytic treatment of power corrections. As for massive event shapes, I will discuss the novel theoretical treatment of secondary radiation of massive quarks, and also the challenges to incorporate primary production. 
Apr 14 2015 
Sandra Eibenberger 
Matterwave interference and quantumassisted metrology with large organic molecules Abstract: Matterwave interferometry can be used to probe the foundations of physics
and to enable precise measurements of particle properties and fundamental
constants. Quantum interference experiments with large molecules have
enabled studies of the quantum superposition principle with particles of
increasing mass and complexity. KapitzaDiracTalbotLau interferometry [1]
has enabled quantum experiments with a wide variety of macromolecules, even
using particles with a mass exceeding 10 000 amu [2]. These experiments
define the currently most stringent bound of the experimental macroscopicity
parameter for quantum superpositions [3]. Typical de Broglie wavelengths of
the investigated particles are in the order of 0.35 pm. This is
significantly smaller than any molecular extension (nanometers) or the
delocalization length in our interferometer (hundreds of nanometers). Many
vibrational and rotational states are populated since the molecules are
thermally highly excited (3001000 K). And yet, highcontrast quantum
interference patterns could be observed. The visibility and position of
these matterwave interference patterns is highly sensitive to external
perturbations. This sensitivity has opened the path to extensive studies of
the influence of internal molecular properties on the coherence of their
associated matter waves. In addition, it enables a new approach to
quantumassisted metrology. I describe how KDTL interferometry can be used
to investigate a number of different molecular properties, including
electric moments [4] and optical absorption cross sections [5].

Apr 21 2015 
Andreas Goudelis 
Aspects of simple dark matter models Abstract: Over the last few decades, the evidence that some relatively nonluminous form of nonbaryonic matter ("dark matter") is dominating the matter content of the universe has piled up. However, essentially all arguments for the existence of dark matter are of a gravitational nature and little is known about its nongravitational properties. I will present a few simple models of particle dark matter and discuss some of their aspects, in particular related to the questions of the dark matter abundance in the universe and its nongravitational detection strategies. 
Apr 28 2015 
Timm Wrase 
Dark Energy and Inflation Abstract: Roughly 70% of the energy density of our current universe is in the form of so called dark energy. While we do not exactly know what this dark energy is, we know that it behaves almost identical to a positive cosmological constant and is responsible for the observed accelerated expansion of our current universe. We also have ample evidence that our very early universe underwent a short period of accelerated expansion that is called inflation. Inflation is sensitive to corrections that cannot be calculated within general relativity coupled to field theory. So in order to understand such corrections we need a UV complete theory of quantum gravity. I will review attempts to construct models that account for the early and late time accelerated expansion of our universe in the context of string theory, which is currently our only contender for a theory of everything. 
May 5 2015 
Emanuele Locatelli 
Dynamical properties of passive and active particles in Single File Abstract: Diffusive passive particle, like colloids, as well as active particles, including bacteria and algae, may happen to be confined in channels so narrow that they cannot overtake each other (Single File conditions). This interesting situation, relevant in Biology, Nanotechnology as well as for water purification and filtration issues, reveals nontrivial physical features as a consequence of the strong interparticle correlations developed in collective rearrangements. We study the dynamical properties of active and passive hard particles under Single File conditions. We propose to sort active particles in two categories: Runners and Tumblers, depending on whether their motion is dominated by straight runs or changes of the directions, respectively. Whereas tumblers’ dynamical behavior reproduces passive (diffusive/Brownian) motion paradigms, runners arrange into clusters which are continuously merging and splitting (living clusters). Finally, in the presence of two absorbing boundaries , by means of analytical techniques, numerical simulations and experiments performed in microfluidic devices, we study the emptying process of the Single File system, i.e. we characterize the progressive decrease of the number of particles, absorbed at the boundaries. 
May 12 2015 
Jakob Salzer 
Twodimensional Dilaton Gravity  A Toy Model for Gravity Abstract: The study of conceptual problems in gravity is often hindered by the technical complexities of general relativity in four dimensions. In such cases it is convenient to have a toy model at one’s disposal that captures the relevant features of general relativity while reducing technical difficulties to a minimum. Twodimensional dilaton gravity is such a model. In this talk I will introduce twodimensional dilaton gravity, describe some of its appealing features and report on some recent work on thermodynamics in this framework. 
May 19 2015 
Josef Pradler 
Light superWIMPs in Astrophysics and Experiment Abstract: More often than not, astrophysical probes are superior to direct laboratory tests when it comes to light, very weekly interacting particles, and it takes clever strategies and/or ultrapure experimental setups for direct tests to be competitive. In this talk, I will highlight this competition on the example of a simple extension of the Standard Model, "Dark Photons." They are a dark matter candidate, and we show how direct detection probes can be superior to stellar constraints. When they decay, cosmology may offer the best sensitivity. 
Jun 2 2015 
Paul Mezgolits 
An introduction to inflation, and how this might work in conformal gravity Abstract: The big bang theory is our best description of the observed universe. Despite its succeses it can not adress key features of the cosmos like the homogeneity and isotropy of our universe and the tiny deviation from this behaviour. The theory of cosmic inflation adresses these issues. My talk will first motivate, and then give a short introduction to, the theory of inflation followed by a discussion of a model of inflation that is based on a theory of gravity that is different from standard Einstein gravity. While inflation is an application of general relativity and quantum field theory, my talk aims to describe the big picture and is accesible to an audience familiar with special relativity and quantum mechanics. 
Jun 9 2015 
Friedrich Schöller 
Heat Kernels and Quantum Gravity Abstract: I give a short introduction to the path integral formulation of quantum mechanics and show how the heat equation can be used to study the semiclassical approximation of a quantum theory. The methods introduced are used to obtain thermodynamic quantities of a three dimensional toy model of quantum gravity. 
Jun 16 2015 
Marco Battiato 
From the discovery to the control of THz spin currents: towards ultrafast spintronics Abstract: The debate over the origin of the ultrafast demagnetization [1] has been intensively active for the past 16 years. Several microscopic mechanisms have been proposed but none has managed so far to provide direct and incontrovertible evidences of their validity. In this context I have proposed an approach based on spin dependent electron diffusion as the driver of the ultrafast demagnetization [2]. Recent experimental findings have revolutionized the field by confirming the existence of spin superdiffusion. We have shown that 1) spin diffusing away from a layer undergoing ultrafast demagnetization can be used to create an ultrafast increase of magnetization [3] in a neighboring magnetic layer, 2) optical excitation is not a prerequisite for the ultrafast demagnetization [4] and that spin unpolarised electrons superdiffusing into a ferromagnetic layer can trigger ultrafast demagnetisation, and 3) superdiffusive spin currents can be tailored by appropriate choice of materials and
used
to produce broadband THz emission via the inverse spin Hall effect [5]. The impact of these new discoveries goes beyond the solution of the mystery of ultrafast demagnetization. It shows how spin information can be, not only manipulated, as shown 16 years ago, but most importantly transported at unprecedented speeds. This new discovery lays the basis for femtosecond spintronics.

Jun 23 2015 
Suchita Kulkarni 
BSM/SUSY phenomenology at the LHC Abstract: The 7 and 8 TeV Run1 of the LHC has brought to us the discovery of a Higgs boson and plethora of results for Beyond the Standard Model (BSM) searches. Even if there has been no evidence of BSM so far, these results are crucial in constraining the parameter space of BSM scenarios. In this talk, I will take a survey of the current existing direct and indirect constraints on Supersymmetry from the LHC and the efforts in the theory world to use these constraints systematically and effectively. I will further illustrate with some case studies, the conclusions that can be derived for SUSY parameter space after LHC Run1. 
Jun 30 2015 
Georg Rohringer 
Critical Properties of Strongly Correlated ManyElectron Systems  A Dynamical Vertex Approximation Study Abstract: Strongly correlated manyelectron systems exhibit a large number of fascinating physical phenomena, such as correlation driven insulating phases, magnetism or hightemperature superconductivity. At the same time, a theoretical description of these systems turns out to be considerably difficult. Hence, one has to adopt approximations in order to calculate experimentally accessible quantities for such systems. In my talk I will introduce the basic models and techniques for treating strong correlations theoretically and describe some of the stateoftheart approximations for solving the manybody problem in this framework. In particular, I will explain how the dynamical mean field theory (DMFT) describes local correlation effects in a lattice exactly. Since in many physical situation also nonlocal correlations play an important role extensions of DMFT are needed. One of such extensions is the Dynamical Vertex Approximation (D$\Gamma$A), which I will introduce. Its applicability for treating strongly correlated electro 
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