Spectral properties at a threshold for two-channel Hamiltonians I. Abstract theory

Spectral properties at thresholds are investigated for two-channel Hamiltonians in various, mostly fairly “singular” settings. In an abstract framework we deduce asymptotic expansions of the resolvent as the spectral parameter tends to a threshold. The results are based on given asymptotic expansions of the component Hamiltonians. Applications to scattering theory are given in a companion paper.