Breit–Wigner series convergence conjecture for super-exponentially decreasing potentials

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Let VV be a super-exponentially decreasing potential, meaning that for every N∈NN\in\mathbf{N}, ∣V(x)∣≲Ne−N∣x∣|V(x)|\lesssim_N e^{-N|x|}. Its Breit–Wigner series is

B(V)=−∑λ∈Res⁡V∖{0}Im⁡λ∣λ∣2.B(V)=-\sum_{\lambda\in\operatorname{Res}V\setminus\{0\}}\frac{\operatorname{Im}\lambda}{|\lambda|^2}.

Breit–Wigner convergence conjecture. The series B(V)B(V) converges if and only if VV is compactly supported.

For compactly supported potentials the series converges, while the conjecture predicts divergence for every super-exponentially decreasing potential that is not compactly supported. This would provide the expected cancellation of infinities in the Breit–Wigner formula as the support becomes unbounded.

References

Primary source

Aidan Backus, “The Breit-Wigner series for noncompactly supported potentials on the line”, arXiv:2005.13765 (2020).

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