Institut für Theoretische Physik
Start / Aktuell / Institut
Dezember  2014
Di
23.12.2014
SR 3, Institut für Theoretische Physik, A03.101
SFB 937
17:15
Seminar



Kontakt: Glormann

Januar  2015
Di
06.01.2015
Seminarraum A3.101
Theoretische Physik
14:15
Theoretisch-physikalisches Seminar

Michael Brockmann
Institute for Theoretical Physics, University of Amsterdam

Two quenches in integrable systems and their non-thermal steady states

In this talk we study quench problems in two different interacting integrable theories. The first one is described by a quench protocol where the ground state of a free many-particle bosonic theory in one dimension is let unitarily evolve in time under the integrable Lieb-Liniger Hamiltonian of δ-interacting repulsive bosons. In the second one the anti-ferromagnetic ordered Néel state, the ground state of the spin-1/2 Ising chain, is quenched to the anisotropic Heisenberg spin chain. By using a variational method, the so-called quench action method, we obtain the exact non-thermal steady-states of the systems in the thermodynamic limit, which correctly reproduce expectation values of local observables. Besides being rare cases of exact solutions to truly interacting quench situations, those two quench protocols represent examples where a naive implementation of the generalized Gibbs ensemble fails.

Kontakt: Stefan Kehrein
Mi
07.01.2015
SR 3, Institut für Theoretische Physik, A03.101
SFB 937
14:15
Seminar

Loredana Casalis

TBA



Kontakt: Glormann
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
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
12.01.2015
Sitzungszimmer Mathematik
Theoretische Physik
14:15

Concepts, familiar from pure states in quantum mechanics, such as "superposition" and "transition probability", are shown to be also meaningful for generic states in infinite systems, described by funnels of type I_\infty algebras. In the physically important case of states of Connes-von Neumann type III_1, these concepts also have a physically significant operational interpretation in terms of primitive observables. (Joint work with Erling St\ormer.)

Kontakt: K.-H. Rehren
Di
13.01.2015
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.

In the first step of fat synthesis, one coenzyme A-activated fatty acid is linked to glycerol-3-phosphate, mainly through the activity of GPAT3, because the knockout mutant has a strikingly “lean” phenotype. Two candidate enzymes for conducting the addition of the second fatty acid, AGPAT3 and PLSC1, failed to affect fat synthesis if knocked out singly or in combination. The third fatty acid is added by enzymes called DGATs. Whereas DGAT2 provides the main activity in mammals, DGAT1 clearly is the dominant enzyme activity in Dictyostelium. Although no defects were observed in a DGAT2 knockout, this protein can restore the defects seen in a DGAT1 KO, if overexpressed.

Most of the above enzymes reside in the Endoplasmic Reticulum when fatty acids are scarce, but move to the surface of lipid droplets when fatty acids are provided in excess. We saw this dual localization also for many other lipid droplets constituents, among these a number of proteins with as yet unknown functions. This step of protein trafficking is remarkable, because the ER is delimited by a normal membrane bilayer, whereas the hydrophobic core of fat in the lipid droplet is surrounded by just a single membrane leaflet. We are currently investigating the basis of the protein redistribution in vivo and in vitro, and the progress will be reported.

Kontakt: Glormann
Mo
19.01.2015
Seminarraum A.04.101
Theoretische Physik
14:15
Quantenfeldtheorie (Forschungsseminar M.Phy.412)

Robert Czechowski
Göttingen

TBA



Kontakt: K.-H. Rehren
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
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.

Kontakt: Stefan Kehrein
Mi
21.01.2015
Seminarraum A 03.101
Theoretische Physik
12:15
Statistische Mechanik komplexer Systeme (Forschungsseminar M.Phy.410)

Alberto Giacomello
Sapienza Università di Roma

Wetting of actual surfaces via atomistic and continuum string methods

The string method is a general and flexible strategy to compute the most probable transition path for an activated process (rare event). I compare here the results for the Cassie-Wenzel transition on a patterned, hydrophobic surface obtained via the atomistic string method in the density field, the continuum "interface" string, and an approximate string, the so-called continuum rare events method. A critical discussion of the three approaches is made, and the physical implacations for superhydrophobicity are analyzed. If time permits, the mechanism of advance and retreat of a liquid front on surfaces with defects will also be discussed as computed from a combination of microscopic DFT and the string method; these results shed light on contact angle hysteresis on anorough surfaces.

Kontakt: Marcus Müller
Do
22.01.2015
Sitzungssaal Mathematik
Theoretische Physik
14:15

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 non-linear 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
Mo
26.01.2015
SR4
Theoretische Physik
14:15
Born-Hilbert-Seminar

Pieter Naajkens
Hannover

TBA



Kontakt: K.-H. Rehren
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

Juni  2015
Di
23.06.2015
SR 3, Institut für Theoretische Physik, A03.101
SFB 937
17:00
Seminar

Tilman Schäffer
Universität Tübingen

TBA



Kontakt: Glormann

Ältere Veranstaltungen im    Archiv
D A P H N E    by Holm
Last modified: Tue May 3 13:27:47 CEST 2011