Conjecture on point spectrum of self-adjoint extensions via Weyl relations

Let the assumptions of hold, with α\alpha the point under consideration, mm and τ\tau the corresponding relations, and A~\widetilde A the self-adjoint extension. For a relation rr, write r(α)r(\alpha) for its value at α\alpha, and call an element nontrivial when it is nonzero.

Point-spectrum conjecture. One has ασp(A~)\alpha\in\sigma_p(\widetilde A) if and only if either there exists a nontrivial element y0y_0 such that

(0;y0)m(α)τ(α),(0;y_0)\in m(\alpha)\cap\tau(\alpha),

or there exists a nontrivial element x0x_0 such that

(x0;0)(m+τ)(α).(x_0;0)\in (m+\tau)(\alpha).

The conjecture proposes that, when mm and τ\tau do not share a pole vector at α\alpha, the cancellation effects seen in earlier counterexamples cannot occur. It characterizes eigenvalues of the self-adjoint extension through common vertical elements of m(α)m(\alpha) and τ(α)\tau(\alpha) or horizontal elements of their sum; the supplied text gives no resolution, so the status remains open.

Sources & referencesView supporting material

Primary source

Annemarie Luger and Jakob Reiffenstein, “On eigenvalues of self-adjoint extensions for defect larger than one”, arXiv:2606.04611 (2026).

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