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arXiv · 2610.29946

Rudin's Problem on Uniformly Bounded Homogeneous Orthonormal Bases

Penghui Wang·Fan Zhang·Zeyou Zhu
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Abstract

Rudin's problem asks whether, in the unit ball of $\mathbb C^d$ with $d\ge2$ fixed, the Hardy space $H^2(\partial\mathbb B_d)$ admits a uniformly bounded orthonormal basis consisting of homogeneous holomorphic polynomials. For $d=2$ and $d=3$ the answer is due to Bourgain, but the general-dimensional case has remained open. This paper gives an affirmative answer to Rudin's problem in every fixed dimension. More precisely, we prove that there is an orthonormal basis consisting of homogeneous polynomials $\{p_j\}_{j=1}^\infty$ of $H^2(\partial\mathbb B_d)$ such that $$\|p_j\|_{L^\infty(\partial\mathbb B_d)}\leq \exp\left(\frac12d\log d+O(d)\right).$$ Here the implicit constant in $O(d)$ is independent of $d$ and $j$.

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Penghui Wang, Fan Zhang, Zeyou Zhu. 2026-10-21. Rudin's Problem on Uniformly Bounded Homogeneous Orthonormal Bases. https://arxiv.org/abs/2610.29946

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