Regensburg 2025 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 19: Many-body Quantum Dynamics I (joint session DY/TT)

TT 19.12: Talk

Tuesday, March 18, 2025, 12:30–12:45, H37

Subleading logarithmic behavior in the parquet formalism — •Marcel Gievers^1,2, Richard Schmidt³, Jan von Delft¹, and Fabian B. Kugler⁴ — ¹Ludwig-Maximilians-Universität, München — ²Max-Planck-Institut für Quantenoptik, Garching — ³Universität Heidelberg — ⁴CCQ, Flatiron Institute, New York

The Fermi-edge singularity in x-ray absorption spectra of metals is a paradigmatic case of a logarithmically divergent perturbation series. Prior work has thoroughly analyzed the leading logarithmic terms. Here, we investigate the perturbation theory beyond leading logarithms and formulate self-consistent equations to incorporate all leading and next-to-leading logarithmic terms. This parquet solution of the Fermi-edge singularity goes beyond the previous first-order parquet solution and sheds new light on the parquet formalism regarding logarithmic behavior. We present numerical results in the Matsubara formalism and discuss the characteristic power laws. We also show that, within the single-boson exchange framework, multi-boson exchange diagrams are needed already at the leading logarithmic level.

Keywords: Feynman diagrams; Computational many-body physics; Fermi-edge singularity; Anderson's orthogonality catastrophe