Legendre Transformation of the Luttinger-Ward Functional from the Bare Interaction Vertex to the Renormalized One

TL;DR

This paper introduces a new Legendre transformation of the Luttinger-Ward functional that expresses the grand potential in terms of the Green's function and a renormalized interaction vertex, enabling unified self-consistent analysis.

Contribution

It develops a novel Legendre transformation to express the grand potential as a functional of Green's function and a renormalized interaction vertex, bridging weak and strong coupling regimes.

Findings

Allows self-consistent calculations of thermodynamic and many-body properties.

Ensures the renormalized vertex reduces to the bare vertex in weak coupling.

Provides a unified framework for studying single- and two-particle properties.

Abstract

On the basis of the Luttinger-Ward functional for interacting many-body systems given in terms of full Green's function $G$ and the bare interaction vertex $\Gamma^{(0)}$, we develop a novel Legendre transformation to express the grand thermodynamic potential $\Omega$ as a functional of $G$ and the renormalized interaction vertex $\Gamma$ so that (i) $G$ and $\Gamma$ obey the stationarity conditions $\delta\Omega/\delta G=0$ and $\delta\Omega /\delta\Gamma=0$ and (ii) $\Gamma$ reduces to $\Gamma^{(0)}$ in the weak-coupling limit. The formalism enables us to perform microscopic studies of thermodynamic, single-particle, and two-particle properties in a unified self-consistent conserving framework.