Institut für Theoretische Physik
Start / Aktuell / Institut
November  2014
Mo
03.11.2014
Sitzungszimmer Mathematik
Theoretische Physik
14:15

We show that Liouville integrable Hamiltonian systems with one-and-a-half degree of freedom can be described by the method of hydrodynamic reductions. The key object is the Vlasov kinetic equation.

Kontakt: K.-H. Rehren
Mi
05.11.2014
Seminarraum A 03.101
Theoretische Physik
12:00
Statistische Mechanik komplexer Systeme (Forschungsseminar M.Phy.410)

Abhinav Sharma
3rd Institute of Physics - Biophysics, Göttingen

Elastic response of Filamentous networks and their remodeling in presence of active forces

My talk will consist of two parts. First I focus on composite networks. Experiments have shown that elasticity of disordered filamentous networks with compliant crosslinks is very different from networks with rigid crosslinks. Filamentous networks are modeled as a collection of randomly oriented rigid filaments connected to each other by flexible crosslinks that are modeled as wormlike chains. We show that for sufficiently high crosslink density, the network linear elastic response is affine on the scale of the filaments’ length. The nonlinear regime can become highly nonaffine and is characterized by a divergence of the elastic modulus at finite strain. In contrast to the prior predictions, we do not find an asymptotic regime in which the differential elastic modulus scales linearly with the stress, although an approximate linear dependence can be seen in a transition from entropic to enthalpic regimes. In the second part of my talk I focus on remodeling of networks in presence of active forces. First we show experimentally that myosin motors contract crosslinked actin polymer networks to clusters with a scale-free size distribution. This critical behaviour occurs over an unexpectedly broad range of crosslink concentrations. To understand this robustness, we developed a quantitative model of contractile networks that takes into account network restructuring: motors reduce connectivity by forcing crosslinks to unbind. Paradoxically, to coordinate global contractions, motor activity should be low. Otherwise, motors drive initially well-connected networks to a critical state where ruptures form across the entire network.

Kontakt: Marcus Müller
Mi
05.11.2014
Seminarraum A 03.101
Theoretische Physik
12:00



Kontakt: Marcus Müller
Fr
07.11.2014
SR 4, Institut für Theoretische Physik, A03.101
SFB 937
14:00
Seminar

Roland Netz
FU Berlin

DNA dynamics, protein force spectroscopy and viscoelastic properties of polymeric networks



Kontakt: Glormann
Mo
10.11.2014
Seminarraum A.04.101
Theoretische Physik
14:15
Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Michael Kiessling
Rutgers Univ. New Brunswick

The Dirac equation and the Kerr-Newman spacetime

I present results obtained jointly with A. Shadi Tahvildar-Zadeh. They concern Dirac's equation for a point electron in the maximal analytically extended Kerr-Newman spacetime in its "zero-gravity limit." In contrast to other "zero-gravity" works, our limit does not yield Minkowski's spacetime decorated with the Appell electromagnetic fields with a physically more-than-questionable ultra-singular "disk source", but instead we obtain a topologically nontrivial Sommerfeld space with meromorphic Appell-Sommerfeld fields that diverge mildly at a ring singularity (boundary of the above-mentioned disk). I explain that the Dirac equation is well-posed on this spacetime in the sense that its associated Hamiltonian is essentially self-adjoint, its spectrum is symmetric, consisting of a continuum with a gap centered at zero in which a discrete spectrum is located if two smallness conditions are met. Some generalizations are addressed also. Finally I explain why our work sheds a new light on some of the most enigmatic aspects of the Dirac equation.

Kontakt: K.-H. Rehren
Do
13.11.2014
Sitzungssaal Mathematik
Theoretische Physik
15:15

A lot of interesting physical and mathematical information about quantum gases at zero temperature in large volume is encoded in the spectral properties of their Hamiltonian and their total momentum. The joint spectrum of these commuting self-adjoint operators can be called the excitation spectrum. One can conjecture that in some situations the excitation spectrum should have an interesting shape characterized by a positive critical velocity, which is related to superfluidity. In my lectures I will discuss heuristic arguments, approximate approaches and rigorous results about excitation spectrum of the Bose interacting gas.

Kontakt: K.-H. Rehren
Fr
14.11.2014
Theoretische Physik
14:00



Kontakt: K.-H. Rehren
Mo
17.11.2014
Sitzungszimmer Mathematik
Theoretische Physik
14:15

A proof of asymptotic completeness of scattering theory for many-body Schroedinger operators has been obtained in the late 80's and early 90's, with contributions of Enss, Sigal, Soffer, Graf and myself. In my opinion it is one of the gems of mathematical physics. It has an interesting history. In my talk I would like to recall the formulation of the problem and sketch various attempts to prove it, including the successful one.

Kontakt: K.-H. Rehren
Di
18.11.2014
SR 3, Institut für Theoretische Physik, A03.101
SFB 937
17:15
Seminar

Frieder Mugele
University of Twente (NL)

TBA



Kontakt: Glormann
Do
20.11.2014
Seminarraum A 03.101
Theoretische Physik
12:00
Statistische Mechanik komplexer Systeme (Forschungsseminar M.Phy.410)

Guojie Zhang
MPI Mainz

Hierarchical Modeling of Highly Entangled Polymer Melts:
Equilibration, Entanglements & Rheology



Kontakt: Marcus Müller
Do
20.11.2014
Sitzungssaal Mathematik
Theoretische Physik
15:15

Motivated by theoretical models in condensed matter physics. We are looking at index theory and spectral flow for operators with essential spectrum (and possibly no discrete spectrum). This talk will survey some of the older and more recent research on this issue.

Kontakt: K.-H. Rehren
Mo
24.11.2014
Seminarraum A.04.101
Theoretische Physik
14:15
Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Simone Dresti
Göttingen

TBA



Kontakt: K.-H. Rehren
Di
25.11.2014
Seminarraum A3.101
Theoretische Physik
14:15
Theoretisch-physikalisches Seminar

Herbert Spohn
TU München

Equilibrium time correlations for anharmonic chains

Since the 1970ies it has been recognized that one-dimensional systems generically have anomalous transport. One manifestation is to consider the super-diffusive spreading of sound and heat peak for the time correlations of the conserved quantities in equilibrium. Recently I proposed a nonlinear extension of fluctuating hydrodynamics to capture the large scale behavior of the correlations. In my talk I will explain the basic theoretical construction and compare with molecular dynamics simulations. The theory amounts to a multi-component extension of the one-dimensional KPZ equation.

Kontakt: J. Oberreuter

Dezember  2014
Mo
01.12.2014
Sitzungszimmer Mathematik
Theoretische Physik
14:15
Born-Hilbert-Seminar

Jan Philip Solovej
University of Copenhagen

TBA



Kontakt: K.-H. Rehren
Di
02.12.2014
SR 3, Institut für Theoretische Physik, A03.101
SFB 937
17:15
Seminar

Yael Roichman
Tel Aviv University

TBA



Kontakt: Glormann
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
15.12.2014
SR4 oder Sitzungszimmer Mathematik
Theoretische Physik
14:15
Born-Hilbert-Seminar

Rainer Verch
Leipzig

TBA



Kontakt: K.-H. Rehren
Di
16.12.2014
Seminarraum A3.101
Theoretische Physik
14:15
Theoretisch-physikalisches Seminar

Markus Heyl
Universität Innsbruck

Many-body localization and quantum ergodicity in disordered long-range Ising model

Ergodicity in quantum many-body systems is —despite its fundamental importance — still an open problem. Many-body 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 long-range interacting Ising models with transverse-field disorder enter a many-body 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 spin-1/2 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

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

Defects in two-dimensional 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 two-dimensional 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
Di
20.01.2015
Seminarraum A3.101
Theoretische Physik
14:15
Theoretisch-physikalisches Seminar

Robin Steinigeweg
Technical University of Braunschweig

Real-time relaxation of currents in spin-1/2 chains: Progress by quantum typicality

We use the concept of typicality to study the real-time dynamics of spin and energy currents in spin-1/2 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 small-system data from exact diagonalization (ED) and existing short-time data from time-dependent 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 long-time 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 high-temperature 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
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 Chern-Simons theory as a fully local field theory in this sense. I show how classical Chern-Simons theory and its "pre-quantization" (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 "p1-structure" (Atiyah 2-framings). 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
Born-Hilbert-Seminar

Jakob Yngvason
Wien

TBA



Kontakt: K.-H. Rehren

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