Spectral variation conjecture for normal operators and differentiator compressions

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Let AA be a normal operator on a complex Hilbert space of dimension n≥2n\ge 2. Let ρ(A)\rho(A) denote the radius of the smallest closed disk containing the spectrum of AA, let A′A' be the compression of AA to the orthogonal complement of a trace vector of AA, and let s(A,A′)s(A,A') denote the spectral variation between AA and A′A'. The spectral variation conjecture. One has

s(A,A′)≤ρ(A),s(A,A')\le \rho(A),

and equality occurs if and only if either A=0A=0, or AA has simple eigenvalues and AnA^n is a non-zero scalar operator. The claim reformulates the polynomial conjectures in terms of spectra of a normal operator and its compression. The source gives no resolution, so the conjecture remains open there.

References

Primary source

Julius Borcea, “Maximal and inextensible polynomials and the geometry of the spectra of normal operators”, arXiv:math/0309233 (2007).

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