@article{22639,
  abstract     = {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.},
  author       = {Desio, Davide and Seiringer, Robert},
  issn         = {1573-0530},
  journal      = {Letters in Mathematical Physics},
  number       = {4},
  publisher    = {Springer Nature},
  title        = {{Dyson expansion for form-bounded perturbations and applications to the polaron problem}},
  doi          = {10.1007/s11005-026-02107-2},
  volume       = {116},
  year         = {2026},
}