# Vienna Theory Lunch Seminar

by Sabine Ertl, Sebastian Frank, Philipp Köhler, Karoline Mühlbacher and Florian Preis

Tuesdays 12:15-13:30

held alternatively at:

TU Wien ( Wiedner Hauptstr. 8-10, yellow area, 10th floor, seminar room E136 )

Uni Wien ( Boltzmanngasse 5, 5th floor, Schrödinger HS / large seminar room )

 11 Oct 2011 TU Wien Patrick Otto Ludl (Uni Wien) Finite family symmetries in the lepton sector Abstract: The fact that at least two of the three known active neutrinos have non-vanishing masses is the most important evidence for physics beyond the standard model of particle physics. In the same way as the introduction of quark mass terms leads to quark mixing, the introduction of neutrino mass terms leads to lepton mixing in charged current interactions. While in the quark-sector the mixing matrix is close to the unit matrix, in the lepton sector this is not the case. In fact in the lepton sector two of the three mixing angles are quite large. An interesting possibility to "explain" these large values for the mixing angles is to impose certain symmetries on the actions of the leptonic and scalar sector, the most popular symmetry groups being finite groups. After an introduction to the physics of lepton mixing we will take a look on the mathematics of finite groups. Finally we will study some simple models using finite groups in order to reproduce some of the features required to accommodate the experimental results. 18 Oct 2011 Uni Wien Dominik Steineder (TU Wien) Holographic View on the Quark Gluon Plasma Abstract: We start by reviewing experimental hints that suggest that the quark gluon plasma, which can be produced in heavy ion collisions taking place at RHIC (Relativistic Heavy Ion Collider) and LHC (Large Hadron Collider) is a strongly coupled liquid rather than a weakly coupled gas. In order to study aspects of this strongly coupled matter we introduce holography also known as gauge gravity duality and calculate the shear viscosity. Finally we discuss the possibilities of studying anisotropic systems within this framework. 25 Oct 2011 TU Wien Michael Gary (TU Wien) Local bulk physics in the AdS/CFT correspondence Abstract: I will review the AdS/CFT correspondence, motivating the duality from the perspective of the black hole information problem. After a thorough introduction, I will explain a test of the holographic nature of the correspondence and show higher dimensional local physics emerging in the limit that the AdS radius becomes large (equivalently, $N_c\rightarrow\infty$). If time allows, I will talk about obstructions to the construction at finite N. 8 Nov 2011 Uni Wien Magdalena Zych (Uni Wien) Quantum interferometric visibility as a witness of general relativistic proper time Abstract: Current attempts to probe general relativistic effects in quantum mechanics focus on precision measurements of phase shifts in matter-wave interferometry. Yet, phase shifts can always be explained as arising due to an Aharonov-Bohm effect, where a particle in a flat space-time is subject to an effective potential. Here we propose a novel quantum effect that cannot be explained without the general relativistic notion of proper time. We consider interference of a "clock" - a particle with evolving internal degrees of freedom - that will not only display a phase shift, but also reduce the visibility of the interference pattern. According to general relativity proper time flows at different rates in different regions of space-time. Therefore, due to quantum complementarity the visibility will drop to the extent to which the path information becomes available from reading out the proper time from the "clock". Such a gravitationally induced decoherence would provide the first test of a genuine general relativistic notion of proper time in quantum mechanics. 22 Nov 2011 TU Wien Jakob Lettenbichler(HEPHY, Uni Wien) Pattern Recognition - Theory and Practice Abstract: The primary goal of current particle physics experiments is to verify/disprove the Standard Model or to find hints for new theories. To be able to do that, a huge number of events has to be recorded and analyzed. Tracks and properties (momentum, type, location of production point (vertex)...) of particles have to be reconstructed from the recorded data to be able to analyze them for statistical deviations from the predictions of current models. A considerable background generated by several effects and geometrical limitations of the detector complicate the task of track reconstruction. In this talk the first step of pattern recognition, the track finding will be presented and explained using the upcoming Belle II - Silicon Vertex Detector at KEK (Japan) as an example. Several common and newer algorithms for that task will be briefly explained. 29 Nov 2011 Uni Wien Stephan Stetina (TU Wien) Superfluidity in dense quark matter Abstract: At very high densities, the ground state of quark matter is a colour superconductor in the "colour flavour locked" (CFL) state. In nature, such densities are realized in compact stars. Since CFL is also a superfluid, properties of compact stars might depend on the hydrodynamics of CFL quark matter. I will therefore discuss, how superfluid hydrodynamics in such a system emerge from the corresponding microscopic theory. 6 Dec 2011 TU Wien Peter Somkuti (TU Wien) The Phenomenology of Yoctosecond Pulses from a Quark-Gluon Plasma Abstract: A quark-gluon plasma formed in heavy-ion collision experiments may feature initial momentum-space anisotropies. Such an anisotropic QGP exhibits a direct photon spectrum which is strongly dependent on the emission angle. Using models for the time evolution of the plasma, a time-dependent photon signal can be calculated whose length is on the order of yoctoseconds. Placing a detector at lower angles close to the beam axis, a photon signal shows a remarkable double-peak shape. In this talk, I will explain the mechanisms that give rise to double pulses, how the effect of such pulses could be observed, and what these pulses can tell us about the quark-gluon plasma itself. 13 Dec 2011 !!!TU Wien at 11:45!!! Toru Kojo (Uni Bielefeld) Chiral Spirals and some issues about chiral symmetry at intermediate quark density Abstract: After a short introduction to QCD and current issues about dense quark matter, I will explain a new state of QCD matter, Quarkyonic matter, which was recently proposed by McLerran and Pisarski. In Quarkyonic matter, quark density is so high that the quarks are released from the baryons, nevertheless excitation modes are confined. After explaining its basic concepts, I will discuss the emergence of the interweaving chiral spirals which spontaneously break the translational, rotational invariance, and the chiral symmetry near the Fermi surface. Its potential relevance to future heavy ion experiments is briefly discussed. 10 Jan 2012 TU Wien Gabriela Mocanu (Babes-Bolyai University, Romania) Stochastic Oscillations of General Relativistic Disks Abstract: The general relativistic oscillations of a thin accretion disk around compact astrophysical objects are analyzed. These objects interact with the surrounding medium through non-gravitational forces, modeled via a friction force and a random force respectively. The dynamics of the stochastically perturbed disk can be formulated in terms of a general relativistic Langevin equation. The vertical oscillations of the disks in the Schwarzschild and Kerr geometries are considered in detail, and they are analyzed by numerically integrating the corresponding Langevin equations. The importance of this analysis in the context of explaining the nontrivial power spectral distribution slopes for Active Galactic Nuclei is discussed. 17 Jan 2012 Uni Wien Igor Pikovski (Uni Wien) Probing Planck-Scale Physics with Quantum Optics Abstract: One of the main challenges in physics today is to merge quantum theory and the theory of general relativity into a unified framework. Various approaches towards developing such a theory of quantum gravity are pursued, but the lack of experimental evidence of quantum gravitational effects thus far is a major hindrance. Yet, the quantization of space-time itself can have experimental implications: the existence of a minimal length scale is widely expected to result in a modification of the Heisenberg uncertainty relation. Here we introduce a scheme that allows an experimental test of this conjecture by probing directly the canonical commutation relation of the center of mass mode of a massive mechanical oscillator with a mass close to the Planck mass. Our protocol utilizes quantum optical control and readout of the mechanical system to probe possible deviations from the quantum commutation relation even at the Planck scale. We show that the scheme is within reach of current technology. It thus opens a feasible route for tabletop experiments to test possible quantum gravitational phenomena. 24 Jan 2012 TU Wien Laura Tolos (Universidad Autonoma de Barcelona) Neutron Stars as Laboratory for Dense Matter Abstract: Neutron stars are an excellent laboratory for testing matter under extreme conditions. In particular, a lot of emphasis has been invested in understanding the interior of neutron stars and the equation of state of the different possible phases since its direct consequences for the mass-radius relationship of neutron stars as well as cooling processes. I will review some results for nucleonic, kaonic and hyperonic matter together with superfluidity and their consequences for cooling processes. I will comment on possible constraints not only from neutron stars observations but also from back-to-Earth experiments, such as heavy-ion collisions. I will finally outline future prospects to be tested in neutron stars laboratory.