“…These results belong to the intersection of two active research topics in spectral and scattering theory. On one hand, resolvent expansions at thresholds (which have a long history, but which have been more systematically developed since the seminal paper of A. Jensen and G. Nenciu [20], see also [11,17,21,28]). On the second hand, representation formulas for the wave operators and their application to the proof of index theorems in scattering theory (see [5,16,23,24,26,27,29] and references therein).…”