Seung-Sup B. Lee: Multipoint correlation functions: spectral representation and numerical evaluation
Title: Multipoint correlation functions: spectral representation and numerical evaluation
Abstract: Four-point correlation functions on the real-frequency axis describe experimentally relevant properties, such as nonlocal susceptibilities, transport, and inelastic photon scattering, of the systems of interacting quantum particles. However, the non-perturbative computation of real-frequency multipoint functions has been intractable. In this talk, I will summarize our recently developed method for non-perturbatively computing multipoint functions and its applications. We have derived generalized spectral representations for multipoint functions that apply in all of the commonly used many-body frameworks: the imaginary-frequency Matsubara and the real-frequency zero-temperature and Keldysh formalisms. We have developed a numerical renormalization group (NRG) method for evaluating the spectral representations for local multipoint functions, which can treat temperatures and frequencies---imaginary or real---of all magnitudes, from large to arbitrarily small ones. I will present the numerical results of four-point vertex functions and resonant inelastic x-ray scattering (RIXS) spectra of quantum impurity systems.