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Equivalence of operator-ideal and Weyl-coefficient criteria in the overlapping order range

Show, by direct computation, whether the conditions obtained via the operator-ideal method for convergence class and type (expressed in terms of integrals of directional entries for diagonal Hamiltonians) are equivalent to the conditions obtained via the Weyl-coefficient approach (expressed in terms of the integral of K_H(t;r)) in the overlapping range of orders between 1 and 2.

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Background

Two complementary approaches yield criteria for dense and sparse spectrum: the operator-ideal method (Part I) provides integral and sequential conditions on the Hamiltonian’s directional entries, while the Weyl-coefficient method (Part I) expresses the Stieltjes transform of the eigenvalue-counting function in terms of an explicit kernel K_H. In the intermediate order regime (between 1 and 2), both sets of criteria apply.

Establishing equivalence would unify the theories and possibly lead to streamlined criteria that are more directly computable from Hamiltonian data.

References

For orders between 1 and 2 we have an overlap with the operator theoretic method from \Cref{U101}. We do not know if one can show equivalence of the respective conditions by direct computation.

Spectral properties of canonical systems: discreteness and distribution of eigenvalues (2504.00182 - Reiffenstein et al., 31 Mar 2025) in Remarks, Section “Trace class and sparse spectrum: the Weyl coefficient approach” (U110)