Dyson expansion for form-bounded perturbations and applications to the polaron problem Desio, Davide ; https://orcid.org/0000-0001-9840-3809 Seiringer, Robert ; https://orcid.org/0000-0002-6781-0521 ddc:510 We present an abstract Dyson expansion for perturbations that are merely relatively form-bounded, and apply it to the polaron problem. For a large class of polaron-type models, including the Fröhlich and Nelson models, we prove that the vacuum expectation value of the heat semi-group is a completely monotone function of the square of the total momentum. Consequently, the ground-state energy is a concave function of the square of the momentum, a result recently proved for the Fröhlich model in [14] using a probabilistic approach via Wiener integrals. Springer Nature 2026 info:eu-repo/semantics/article doc-type:article text http://purl.org/coar/resource_type/c_2df8fbb1 https://research-explorer.ista.ac.at/record/22639 https://research-explorer.ista.ac.at/download/22639/22641 Desio D, Seiringer R. Dyson expansion for form-bounded perturbations and applications to the polaron problem. <i>Letters in Mathematical Physics</i>. 2026;116(4). doi:<a href="https://doi.org/10.1007/s11005-026-02107-2">10.1007/s11005-026-02107-2</a> eng info:eu-repo/semantics/altIdentifier/doi/10.1007/s11005-026-02107-2 info:eu-repo/semantics/altIdentifier/issn/1573-0530 info:eu-repo/semantics/altIdentifier/arxiv/2512.13443 info:eu-repo/semantics/openAccess