Seminare über Quantenfeldtheorie

Kontakt: Tretyakov

Kontakt: K.-H. Rehren

Kontakt: Prof. A. Zippelius

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Glass transitions are associated with a rapid increase of the relaxation time in a system as a function of an external parameter, usually temperature or volume fraction. When the relaxation time becomes longer than the typical experimental timescale, phenomena associated with the absence of thermodynamic equilibrium start to become evident. In the regime near the glass transition, materials exhibit "dynamical heterogeneity", i.e., the presence of correlated fluctuations in the dynamical behavior of small regions of the system, whose origin is still poorly understood. One possible theoretical approach to explain the origin of these fluctuations involves the presence of local fluctuations in the time variables. This picture can be also seen to emerge from a simple phenomenological description of dynamical heterogeneity in terms of fluctuating local relaxation times. I will present Molecular Dynamics simulation results characterizing the statistical properties of the fluctuations in models of structural glasses, both in equilibrium and out of equilibrium. These results exhibit evidence for the presence of universality, scaling behavior, and a dynamic correlation length that grows as the system relaxes; and they are consistent with a description of dynamical heterogeneity in terms of fluctuations of the time variables.

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

We consider thermal states on one-dimensional conformal theories. In our previous work, we showed that completely rational nets admit only one KMS state at each temperature. Here the subject is non rational nets. We construct and completely classify KMS states on U(1)-current net and the Virasoro net with c=1. We explain how nontrivial KMS states could lead to new Moebius covariant nets.

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Ich werde grundlegende Bemerkungen zur Nicht-Voraussagbarkeit der Zukunft in relativistischen Theorien und zum Indeterminismus der Quantentheorie machen. Anschliessend werde ich einen einheitlichen Formalismus zur Beschreibung klassischer und quantenmechanischer physikalischer Systeme skizzieren und die radikalen Unterschiede zwischen klassischer und Quantenphysik andeuten. Schliesslich soll dargelegt werden, wie die Geometrie der Raum-Zeit in der Quantentheorie erscheint.

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

In colloidal suspensions, self-assembly and self-organization processes can be easily fueled by external fields. Here we discuss recent computer simulation and theoretical results for the dynamical behavior of suspensions of ferromagnetic particles under the influence of (static and time-dependent) magnetic fields. In the first part we discuss the translational diffusion in static fields, where the particles tend to aggregate into chains. We show that the anisotropic, yet normal diffusive behavior seen in weakly coupled systems and finite fields can become anomalous both parallel and perpendicular to the field at sufficiently large coupling strengths. The second part focusses on the impact of rotating fields. Here one observes both synchronized states, where the individual particles follow the field with (on average) constant phase difference, and asynchronous states. Depending on the spatial dimension, the synchronization is accompanied by layer formation, i.e. by spatial symmetry-breaking, or by a clustering process.Our suggest that these pattern formation phenomena can be understood, at least partially, as by-products of an equilibrium phase transition.

Kontakt: A. Zippelius

Questions hour (14:15): Introduction to modern measurement theory and Ozawa's new formulation of the uncertainty relation

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Motivated by the study of quantum quenches in integrable field theories (IFTs) and in particular the structure of the initial state after such a quench, we are led to the investigation of transformations of the Zamolodchikov-Faddeev operators that respect their algebra. After showing that, unlike in free theories, linear transformations (Bogoliubov transformations) do not satisfy this condition, we explore simple cases of infinitesimal transformations that do so and study their properties. Examples from typical IFTs like the Sinh-Gordon and Lieb-Liniger models are presented, emphasizing the possibility to study quantum quenches.

Kontakt: Stefan Kehrein

Kontakt: K.-H. Rehren

Kontakt: Thomas Pruschke

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren

Kontakt: K.-H. Rehren