An arbitrary-size cyclic weighted-shift conjecture for higher numerical ranges

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Let FB∈C[t,x,y]dCnF_B\in\mathbb{C}[t,x,y]^{C_n}_d be the homogeneous polynomial associated with a matrix B∈Cd×dB\in\mathbb{C}^{d\times d}, and let Wk(B)\mathcal{W}_k(B) denote its kk-th numerical range. Let CC(n,d)\mathcal{C}_{\mathbb{C}}(n,d) denote the class of cyclic weighted shift matrices of size dd with cyclic structure parameter nn. Higher numerical-range realization conjecture. There exists A∈CC(n,d)A\in\mathcal{C}_{\mathbb{C}}(n,d) such that

Wk(A)=Wk(B)for all 1≤k≤⌊d/2⌋+1.\mathcal{W}_k(A)=\mathcal{W}_k(B)\qquad\text{for all }1\leq k\leq\left\lfloor d/2\right\rfloor+1.

The corollary proves this after replacing dd by n⌈d/n⌉n\lceil d/n\rceil; extending the theorem to arbitrary dd would imply the stated same-size realization, which remains unproved in the supplied text.

References

Primary source

Faye Pasley Simon and Cynthia Vinzant, “Invariant hyperbolic curves: determinantal representations and applications to the numerical range”, arXiv:2102.01726 (2021).

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