HIGHER ORDER CORRECTIONS TO PARTICLE-HOLE SPECTRA USING GREEN'S FUNCTION TECHNIQUES.

D. Husain

A. Maquet

We present a calculation of the radiative shifts and broadenings of the energy levels of a hydrogenic atom, irradiated by a strong, non-resonant and monomode laser field. The calculation is performed within the framework of the timedependent perturbation theory, up to fourth-order included, using the sturmian representation of the Coulomb Green's function. The order of magnitude of these corrections as well as several interesting limiting cases are considered and discussed.

Gabriele Riva, Théodore Fischer, Stefano Paggi +2 more

Recently we proposed a multichannel Dyson equation, in which we coupled the one- and the three-body Green's functions, to model photoemission spectra. In this work we extend this concept to higher-order Green's functions and to other spectroscopies. We show the general structure of the equations and how one can systematically approximate the corresponding multichannel self-energy. As a particular case, we focus on the coupling of the two-body and the four-body Green's functions in the electron-hole channel to describe neutral excitations. This formulation allows for the description of important many-body effects, such as biexcitons, in a natural way. We illustrate our approach by applying it to a two-level model system, which, in a one-particle picture, exhibits single and double excitations. Our method can correctly describe both kinds of excitation, unlike standard approaches, and in good agreement with the exact results.

Eleftherios N. Economou