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Q: Quantenoptik

Q 301: Poster: Fallen, Kühlung, Teilchenoptik

Q 301.37: Poster

Wednesday, March 6, 2002, 11:00–13:00, Schloss

Non-analytic vertex renormalization in thermal Bose-Einstein condensation — •Georgios Metikas and Gernot Alber — Abteilung für Quantenphysik, Universität Ulm, D-89069 Ulm, Germany

At finite temperature, when an effective theory is derived from an underlying theory by means of perturbation over the coupling and derivative expansion over the slowly varying field, graphs which are of second or higher order in the coupling may exhibit non-analytic behaviour at the origin of the momentum-frequency space provided the internal propagators are mass-degenerate. The most well-known example of this behaviour occurs in the dressed photon propagator in thermal QED and leads to the phenomena of Debye screening and plasma oscillations. Since an essential step of the renormalization group method is to integrate out the fields with Fourier components in an infinitesimal momentum shell near the cutoff and thus create an effective action for the fields with Fourier components below this shell, we anticipate that, when renormalization is used at finite temperature, certain graphs of the effective theory will exhibit non-analytic behaviour. As an example we examine what happens when we apply renormalization techniques to a homogeneous, dilute, interacting BEC. It turns out that the non-analyticity appears in the renormalized four-boson vertex. The consequences of this phenomenon to the universal and non-universal properties of the BEC are then explored and the physical meaning of the vertex non-analyticity discussed.