Banded perturbation conjecture for twisted Toeplitz matrices

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Let a(x,z)a(x,z) be the symbol on [0,1]×T[0,1]\times\mathbb{T}

a(x,z)=∑j=−qpaj(x)zj,a(x,z)=\sum_{j=-q}^p a_j(x)z^j,

where aj(x)a_j(x) are continuous complex-valued functions on [0,1][0,1]. Let Rn(a)=Tn(a)+σnXnR_n(a)=T_n(a)+\sigma_nX_n be the structured random perturbation described above, and let νx\nu_x be the weak limit of the eigenvalue-counting measures of the frozen Toeplitz matrices Tn(ax)T_n(a_x), where ax=a(x,⋅)a_x=a(x,\cdot). Define

μn=1n∑λ∈sp⁡(Rn(a))δλ.\mu_n=\frac{1}{n}\sum_{\lambda\in\operatorname{sp}(R_n(a))}\delta_\lambda.

Banded perturbation conjecture. The measures μn\mu_n converge weakly to

μ=∫01νx dx.\mu=\int_0^1\nu_x\,dx.

This conjecture extends the tridiagonal random-perturbation spectral asymptotics to banded twisted Toeplitz matrices, predicting that the limiting eigenvalue distribution is obtained by averaging the limiting measures of the frozen symbols. Its status is not resolved in the supplied source.

References

Primary source

Dario Giandinoto and Boris Shapiro, “Structured perturbations of tridiagonal twisted Toeplitz matrices”, arXiv:2604.20617 (2026).

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