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arXiv · 2609.37180

Polynomial Counterexamples to Shanks' Conjecture in Dirichlet-Type Spaces over the Bidisc

Oliver Navío·Daniel Seco
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Abstract

We study optimal polynomial approximants in spaces of Dirichlet-type over the bidisc. Given a nonzero function f, the linear optimal polynomial approximant (opa) to its reciprocal is the affine polynomial p for which pf is closest to the constant function 1 in the space norm. We prove that, for every positive value of the Dirichlet-type parameter, there exists a symmetric polynomial f with no zeros on the closed bidisc, while the corresponding linear optimal approximant has a zero inside the bidisc. This provides polynomial counterexamples to the version of the Weak Shanks Conjecture on these spaces. The construction also extends to higher-dimensional polydiscs and to anisotropic Dirichlet-type spaces.

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BibTeXRIS

Oliver Navío, Daniel Seco. 2026-09-29. Polynomial Counterexamples to Shanks' Conjecture in Dirichlet-Type Spaces over the Bidisc. https://arxiv.org/abs/2609.37180

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