Schwinger-Keldysh effective actions for non-hydrodynamic poles and branch cuts
Abstract
Retarded thermal correlators, analytically continued to complex frequency, exhibit non-hydrodynamic poles and branch cuts that constrain hydrodynamics. We construct Gaussian Schwinger-Keldysh effective actions in which branch cuts arise from continua of relaxation poles and response functions are governed by Stieltjes transforms of relaxation-time densities. Dynamical KMS symmetry, positivity and stability constrain the spectra, while endpoint behaviour controls the local branch structure and near-edge pole scaling. The illustrative examples of uniform and power-law densities exhibit respectively beyond-all-orders pole-endpoint separation and a continuous interpolation between pole-pole and pole-branch-point termination. Finally, we show that an energy-dependent relaxation-time approximation in kinetic theory provides a microscopic realization of our branch cuts at zero momentum.
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BibTeX
@misc{amoretti2026schwingerkeldysh,
title = {{Schwinger-Keldysh effective actions for non-hydrodynamic poles and branch cuts}},
author = {Andrea Amoretti and Matteo Anselmi and Daniel K. Brattan},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.16164},
eprint = {2609.16164},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.16164},
}
RIS
TY - UNPB
TI - Schwinger-Keldysh effective actions for non-hydrodynamic poles and branch cuts
AU - Andrea Amoretti
AU - Matteo Anselmi
AU - Daniel K. Brattan
PY - 2026
DA - 2026/09/24
PB - arXiv
DO - 10.48550/arxiv.2609.16164
UR - https://arxiv.org/abs/2609.16164
AB - Retarded thermal correlators, analytically continued to complex frequency, exhibit non-hydrodynamic poles and branch cuts that constrain hydrodynamics. We construct Gaussian Schwinger-Keldysh effective actions in which branch cuts arise from continua of relaxation poles and response functions are governed by Stieltjes transforms of relaxation-time densities. Dynamical KMS symmetry, positivity and stability constrain the spectra, while endpoint behaviour controls the local branch structure and near-edge pole scaling. The illustrative examples of uniform and power-law densities exhibit respectively beyond-all-orders pole-endpoint separation and a continuous interpolation between pole-pole and pole-branch-point termination. Finally, we show that an energy-dependent relaxation-time approximation in kinetic theory provides a microscopic realization of our branch cuts at zero momentum.
ER -