Dezember 2014  
Mo 
01.12.2014
Sitzungszimmer Mathematik
Theoretische Physik

14:15 
Kontakt:
K.H. Rehren

Mo 
01.12.2014
Seminarraum A3.101
Theoretische Physik

14:15 
Aktuelle Probleme der theoretischen Festkörperphysik
(Forschungsseminar M.Phy.411)
Manuel Kreye Universität Göttingen
'The Unruh Effect in Condensed Matter' We want to understand (quantum) phase transitions in nonequilibrium where recent progress has been made in the field of quantum quench dynamics. One open question is, under what circumstances a quenched system reaches a stationary state and whether this can be described by a thermal density matrix. There is an interesting formal analogy between quantum quenches and the transformation to uniformly accelerating coordinate frames. In the latter the Unruh effect is observed that predicts a thermal distribution in the accelerating frame while in the rest frame there is none. A short overview of the theoretical foundations of the Unruh effect will be given and some analogies to quantum quenches will be explored. Kontakt:
S. Kehrein

Di 
02.12.2014
SR 3, Institut für Theoretische Physik, A03.101
SFB 937

17:15 
Seminar
Yael Roichman University of Tel Aviv
Dynamics in Steady State inVitro ActoMyosin Networks We show that complex fluids such as actin networks respond to deformations differently at intermediate length scales than they do as a bulk material, at large distances. When characterizing passive entangled Factin networks we found that this intermediate response regime, characterized by an decay with distance, persists to surprisingly large distances of 26 µm, which is comparable the size of a cell, and over ten times larger than the mesh size of the actin network. A similar crossover was observed previously in microtubule networks at r_c = 15 µm, if not as clearly, and without explanation. We use this newfound understanding to extract structural information of active invitro reconstituted cytoskeleton networks, in which such analysis can be done in a controlled fashion. Kontakt:
Glormann

Mi 
03.12.2014
Seminarraum A 03.101
Theoretische Physik

12:00 
Statistische Mechanik komplexer Systeme (Forschungsseminar M.Phy.410)
Qiyun Tang Göttingen
Physical Aging in Ultrathin Polymer Films: A Molecular Simulation Study Physical aging in glassy polymer films has attracted great attention in the past two decades due to their strong correlation with the lifetime of polymerbased nanodevices. Recently we developed a simulation routine by introducing vacancy diffusion and annihilation processes into the Monte Carlo simulation to study these phenomena. We found that the responses of film aging rates to temperatures are consistent with that for glassy polymer films in experiments. Especially, we demonstrated that the accelerated physical aging, commonly observed in experiments, slows down at extremely small film thicknesses. This phenomenon can be attributed to an inversed vacancy diffusion process caused by the sliding motion of chain molecules. Our findings provide direct evidence of the relationship between the sliding motion of short chain fragments and the physical aging of ultrathin polymer films, and also verify the existence of a new confinement effect at the nanoscale. Kontakt:
Marcus Müller

Mo 
08.12.2014
Seminarraum A.04.101
Theoretische Physik

14:15 
Quantenfeldtheorie (Forschungsseminar M.Phy.412)
Federico Dradi Göttingen
TBA Kontakt:
K.H. Rehren

Mo 
08.12.2014
Seminarraum A3.101
Theoretische Physik

14:15 
Aktuelle Probleme der theoretischen Festkörperphysik
(Forschungsseminar M.Phy.411)
Debanjan Basu Institute for Theoretical Physics Technical University Clausthal
Complex Bandstructure for calculating Thermal Conductivity across Nanostrucutred Interfaces Thermal conductivity is an important factor affecting the efficiency of thermoelectric devices. Our goal is to explore the thermal transmission due to phonons in multilayered structures on a modebymode basis using the Beam Matching Technique. For this purpose, we determine the “complex bandstructure”, which describes propagating as well as evanescent phonon modes of the individual materials of this multilayer.We describe how to extract the matching conditions from the classical equations of motion for the atoms. Kontakt:
S. Kehrein

Mo 
15.12.2014
SR4 oder Sitzungszimmer Mathematik
Theoretische Physik

14:15 
Kontakt:
K.H. Rehren

Mo 
15.12.2014
Seminarraum A3.101
Theoretische Physik

14:15 
Aktuelle Probleme der theoretischen Festkörperphysik
(Forschungsseminar M.Phy.411)
Benjamin Lenz Universität Göttingen
TBA TBA Kontakt:
S. Kehrein

Mo 
15.12.2014
HS 4
SFB 937

14:15 
Seminar
Peter J.M. van Haastert University of Groningen, The Netherlands
How cells move and navigate in shallow gradients of chemoattractant Central to chemotaxis is the molecular mechanism by which a shallow spatial gradient of chemoattractant induces protrusions in the direction of the gradient. We use Dictyostelium to investigate the minimal requirements for chemotaxis, and identified a basal signaling module providing activation of Ras and Factin at the leading edge. I will present a conceptual framework of gradient sensing and chemotaxis that is based on basal cell movement with on top of that a directional bias by the cAMP gradient. In the absence of external cues, cells extend protrusions in an ordered stochastic process with a mixture of alternating rightleft splitting of an existing protrusion, by which cells move persistently in one direction, and extension of new protrusions in random directions. The place where these protrusions are formed is highly associated with patches of activated Ras. A cAMP gradient induces the local activation of Ras at the side of the cell facing the highest concentration of cAMP. In shallow gradients, this cAMPinduced activated Ras combines with endogenous Ras activation to increase the probability to extend protrusions in the direction of the cAMP gradient. Other signaling pathway such as PI3K, TORC2 and guanylyl cyclace/myosin contribute to chemotaxis as memory of direction and amplifiers of spatial information. Kontakt:
Glormann

Di 
16.12.2014
Seminarraum A3.101
Theoretische Physik

14:15 
Theoretischphysikalisches Seminar
Markus Heyl Universität Innsbruck
Manybody localization and quantum ergodicity in disordered longrange Ising model Ergodicity in quantum manybody systems is —despite its fundamental importance — still an open problem. Manybody localization provides a general framework for quantum ergodicity, and may therefore offer important insights. In this talk, it will be shown using both numerical and analytical methods that longrange interacting Ising models with transversefield disorder enter a manybody localized phase at infinite temperature, irrespective of the disorder strength. As a consequence, these systems are nonergodic. To characterize and quantify quantum ergodicity, a measure for distances in Hilbert space will be introduced. It will be shown that in spin1/2 systems it is equivalent to a simple local observable in real space, which can be measured in current experiments of superconducting qubits, polar molecules, Rydberg atoms, and trapped ions. Kontakt:
S. Kehrein

Do 
18.12.2014
Sitzungssaal Mathematik
Theoretische Physik

15:15 
We study harmonic maps between hyperbolic spaces. In particular, we focus on a famous conjecture due to Rick Schoen. According to this conjecture every quasisymmetric map: S^{1} to S^{1} can be uniquely extended to a quasiconformal harmonic diffeomorphism: D^{2} to D^{2}, where here D^{2} stands for the unit open disk of R^{2} equipped with the hyperbolic metric. The uniqueness has been settled by Li and Tam. However, the existence part remains still open. We shall confirm affirmatively the conjecture if we impose some additional conditions on the initial data. Kontakt:
K.H. Rehren

Januar 2015  
Mo 
05.01.2015
Seminarraum A.04.101
Theoretische Physik

14:15 
Quantenfeldtheorie (Forschungsseminar M.Phy.412)
Robert Czechowski Göttingen
TBA Kontakt:
K.H. Rehren

Do 
08.01.2015
Sitzungssaal Mathematik
Theoretische Physik

15:15 
Graduiertenkolleg 1493
Ingo Runkel Hamburg
Orbifolds and spin structures from defects in twodimensional field theories Defects in twodimensional quantum field theories are lines across which fields of the theory may have discontinuities. Such defects are called "topological" if their precise location does not matter when evaluating correlators. Topological defects contain a lot of information about the field theory in question. In this talk I will concentrate on twodimensional topological and conformal field theories, and I would like to explain how two superficially quite different constructions turn out to be closely related when formulated via defects. These are 1) the orbifolding procedure, and 2) building field theories on surfaces with spin structure. Kontakt:
K.H. Rehren

Mo 
12.01.2015
Seminarraum A3.101
Theoretische Physik

14:15 
Aktuelle Probleme der theoretischen Festkörperphysik
(Forschungsseminar M.Phy.411)
David Storch Universität Göttingen
TBA TBA Kontakt:
S. Kehrein

Mo 
19.01.2015
Seminarraum A3.101
Theoretische Physik

14:15 
Aktuelle Probleme der theoretischen Festkörperphysik
(Forschungsseminar M.Phy.411)
Ingo Homrighausen Universität Göttingen
TBA TBA Kontakt:
S. Kehrein

Di 
20.01.2015
Seminarraum A3.101
Theoretische Physik

14:15 
Theoretischphysikalisches Seminar
Robin Steinigeweg Technical University of Braunschweig
Realtime relaxation of currents in spin1/2 chains: Progress by quantum typicality We use the concept of typicality to study the realtime dynamics of spin and energy currents in spin1/2 models in one dimension and at nonzero temperatures [1,2]. These chains are the integrable XXZ chain and a nonintegrable modification due to the presence of a staggered magnetic field oriented in z direction. In the framework of linear response theory, we numerically calculate autocorrelation functions by propagating a single pure state, drawn at random as a typical representative of the full statistical ensemble. By comparing to smallsystem data from exact diagonalization (ED) and existing shorttime data from timedependent density matrix renormalization group (tDMRG), we show that typicality is satisfied in finite systems over a wide range of temperature and is fulfilled in both, integrable and nonintegrable systems. For the integrable case [1], we calculate the longtime dynamics of the spin current and extract the spin Drude weight for large systems outside the range of ED. We particularly provide strong evidence that the hightemperature Drude weight vanishes at the isotropic point. For the nonintegrable case [2], we obtain the full relaxation curve of the energy current and determine the heat conductivity as a function of magnetic field, exchange anisotropy, and temperature. 
Do 
22.01.2015
Sitzungssaal Mathematik
Theoretische Physik

14:15 
Graduiertenkolleg 1493
Igor Khavkine Trento
Analyticity is an unnecessary hypothesis in the renormalization of locally covariant QFT Finite renormalization freedom in locally covariant quantum field theories on curved spacetime is known to be tightly constrained, under certain standard hypotheses, to the same terms as in flat spacetime up to finitely many curvature dependent terms. These hypotheses include locality, covariance, scaling, and continuous and analytic dependence on the metric and coupling parameters. The analytic dependence hypothesis is somewhat unnatural, because it requires that locally covariant observables (which are simultaneously defined on all spacetimes) depend continuously on an arbitrary metric, with the dependence strengthened to analytic on analytic metrics. Moreover the fact that analytic metrics are globally rigid makes the implementation of this requirement at the level of local algebras of observables rather technically cumbersome. We show that the conditions of locality, covariance and scaling, in conjunction with the microlocal spectral condition, are actually sufficient to constrain the allowed finite renormalizations equally strongly, making both the continuity and the analyticity hypotheses unnecessary. The key step in the proof uses the nonlinear Peetre theorem on the characterization of differential operators. Based on [arXiv:1411.1302]. Kontakt:
K.H. Rehren

Mo 
26.01.2015
Seminarraum A3.101
Theoretische Physik

14:15 
Aktuelle Probleme der theoretischen Festkörperphysik
(Forschungsseminar M.Phy.411)
Davide Fioretto Universität Göttingen
TBA TBA Kontakt:
S. Kehrein

Di 
27.01.2015
SR 3, Institut für Theoretische Physik, A03.101
SFB 937

17:15 
Seminar
Markus Maniak University of Kassel
Biogenesis of Lipid Droplets from the Endoplasmic Reticulum If grown axenically, Dictyostelium amoebae fail to build one cellular organelle, the lipid droplet. As soon as free fatty acids are added to the growth medium, or when amoebae are fed with bacteria, fat synthesis begins and lipid droplets are formed.
Kontakt:
Glormann

Do 
29.01.2015
Sitzungssaal Mathematik
Theoretische Physik

15:15 
The cobordism hypothesis classifies fully local topological field theories. It is an open problem to realize quantum ChernSimons theory as a fully local field theory in this sense. I show how classical ChernSimons theory and its "prequantization" (in the sense of geometric quantization) has a fully local incarnation, and how it implies the need to cancel the quantum anomaly by means of "p1structure" (Atiyah 2framings). I close with an outlook on how this could be used to get the fully local quantum theory. Kontakt:
K.H. Rehren

Februar 2015  
Mo 
23.02.2015
SR4 oder Sitzungszimmer Mathematik
Theoretische Physik

14:15 
Kontakt:
K.H. Rehren
