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DY: Fachverband Dynamik und Statistische Physik

DY 2: Statistical Physics (General)

DY 2.6: Vortrag

Montag, 26. März 2012, 11:15–11:30, MA 004

An extension of the derivative expansion of the exact renormalization group to finite momenta — •Nils Hasselmann — MPI f. Festkörperforschung, Heisenbergstr. 1, D-70569 Stuttgart

The non-perturbative renormalization group (NPRG) technique is based on an exact fow equation of the effective average action. It has proved especially useful when applied to critical phenomena. While the exact flow equation of the effective average action can almost never be solved, it allows for novel approximation techniques which are indeed non-perturbative. One rather successful approximation strategy is the derivative expansion, where the effective average action is expanded consistently to a given order in spatial derivatives, but no truncation is made in the power of the fields.

Here we present a simple truncation scheme of the exact flow equations for the effective action which allows to access the full momentum structure of vertices while at the same time reproducing the results of a leading order derivative expansion of the action, where local correlations are kept to infinite order in the fields. Different to existing schemes to calculate momentum dependent vertices, in our scheme all approximations are done at the level of the effective action which is generally better than truncating the flow equations of a field expansion. As an example for the feasibility of the technique, we present results for the O(n) model.