Cyclicity threshold conjecture for polynomials in Dirichlet-type spaces of the unit ball

Let Bn\mathbb B_n be the unit ball in Cn\mathbb C^n, let Sn\mathbb S_n be its boundary sphere, and let Z(p)\mathcal{Z}(p) denote the zero set of a polynomial pp. A polynomial is cyclic in Dα(Bn)D_\alpha(\mathbb B_n) if the polynomials obtained by multiplying it by elements of the polynomial algebra are dense in Dα(Bn)D_\alpha(\mathbb B_n). Let pC[z1,,zn]p\in\mathbb C[z_1,\dots,z_n] be a polynomial with no zeros in Bn\mathbb B_n. Suppose that Z(p)Sn\mathcal{Z}(p)\cap\mathbb S_n contains a real submanifold of R2n\mathbb R^{2n} of dimension m1m-1, where m=2,3,,nm=2,3,\dots,n, but contains no submanifold of any higher dimension. Cyclicity conjecture. Then pp is cyclic in Dα(Bn)D_\alpha(\mathbb B_n) if and only if

α2n(m1)2.\alpha\le\frac{2n-(m-1)}{2}.

The conjecture extends the known characterization for the model polynomials 1mm/2z1zm1-m^{m/2}z_1\cdots z_m, whose boundary zero sets have real dimension m1m-1. It predicts that the maximal real dimension of the boundary zero set determines the precise cyclicity threshold for arbitrary zero-free polynomials, while the claim remains unresolved in the stated generality.

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Primary source

Dimitrios Vavitsas and Konstantinos Zarvalis, “Non-cyclicity and polynomials in Dirichlet-type spaces of the unit ball”, arXiv:2405.03020 (2024).

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