Coupling Constant Thresholds in Nonrelativistic Quantum Mechanics. I. Short-Range Two-Body Case

Consider −Δ + λV with V short range at a value λ_0 where some eigenvalue e(λ) → 0 as λ ↓ λ_0. We analyze two questions: (i) What is the leading order of e(λ), i.e., for what α does e(λ) ∼ c(λ − λ_0)^α? (ii) Is e(λ) analytic at λ = λ_0 and, if not, what is the natural expansion parameter? The results are highly dimension dependent