Response theory for quantum fields in isolation

Quantum Physics [Submitted on 15 Apr 2026] Response theory for quantum fields in isolation Stefan Floerchinger Response theory describes the reaction of observales to perturbations in external fields. We review this formalism for quantum fiels in isolation that have unitary time evolution. An emphasis is put on consequences of causality and the resulting spectral representations for linear and nonlinear response functions, on functional techniques and generating functionals, including the description of the initial state, the evolution, and measurements. We review consequences of time reversal symmetry and relations for the statistics of work, and discuss a large class of quantum correlation functions, and their relation to response functions through fluctuation-dissipation relations. Consequences of conservation laws and gauge symmetries are mentioned briefly. Comments: 56 pages, 2 figures Subjects: Quantum Physics (quant-ph); High Energy Physics - Theory (hep-th); Nuclear Theory (nucl-th) Cite as: arXiv:2604.13637 [quant-ph]   (or arXiv:2604.13637v1 [quant-ph] for this version)   https://doi.org/10.48550/arXiv.2604.13637 Focus to learn more Submission history From: Stefan Floerchinger [view email] [v1] Wed, 15 Apr 2026 09:03:46 UTC (61 KB) Access Paper: HTML (experimental) view license Current browse context: quant-ph < prev   |   next > new | recent | 2026-04 Change to browse by: hep-th nucl-th References & Citations INSPIRE HEP NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)