New many body perturbation method and the Hubbard model

Reiner M. Dreizler, Eberhard K. U. Gross

Cláudio Andrade Macedo, M. D. Coutinho Filho

We are able to demonstrate that we can attain a proper comprehension of the functional-integral method as applied to the Hubbard and similar model systems. This is done in the context of diagrammatic perturbation theory. In particular, new as well as well-known exact relations among physical quantities of interest are derived in the context of the formalism.

Yoshio Kuramoto

Mukherjee, Abhishek, M. Cristoforetti

Recently, a new method, based on stochastic integration on the surfaces of steepest descent of the action, was introduced to tackle the sign problem in quantum field theories. We show how this method can be used in many body theories to perform fully non-perturbative calculations of quantum corrections about mean field solutions. We discuss an explicit algorithm for implementing our method, and present results for the repulsive Hubbard model away from half-filling at intermediate temperatures. Our results are consistent with those from the recent state of the art cluster dynamical mean field theory calculations.

S. Pairault, David Sénéchal, A.–M. S. Tremblay

Samuel P. Bowen

A generalization of Feenberg's Perturbation Theory is shown to give exact expressions for the temperature dependent retarded greens functions for a many body problem. The theorem establishing this relationship is sketched and the result briefly applied to the Hubbard model.