Chui's equispaced-poles conjecture in the Bergman space

Let D\mathbb D be the unit disk and let L1(D)L^1(\mathbb D) denote the space of integrable functions on D\mathbb D with respect to normalized planar Lebesgue measure. For a positive integer NN and points a0,,aN1a_0,\ldots,a_{N-1} on the unit circle, consider the simplest fraction 0k<N(zak)1\sum_{0\le k<N}(z-a_k)^{-1}. Chui's conjecture. For every positive integer NN and every family of points {ak}0k<N\{a_k\}_{0\le k<N} on the unit circle,

0k<N1zakL1(D)0k<N1ze2πik/NL1(D).\left\|\sum_{0\le k<N}\frac{1}{z-a_k}\right\|_{L^1(\mathbb D)}\ge \left\|\sum_{0\le k<N}\frac{1}{z-e^{2\pi i k/N}}\right\|_{L^1(\mathbb D)}.

Equivalently, among simplest fractions with NN poles on the unit circle, the one with equispaced poles has minimal L1(D)L^1(\mathbb D) norm. The paper's abstract states that this conjecture is solved for a wide class of weighted Hilbert Bergman spaces, while the displayed L1L^1 formulation is presented as Chui's original conjecture; the supplied text does not state that this exact formulation has been resolved.

Sources & referencesView supporting material

Primary source

Evgeny Abakumov, Alexander Borichev and Konstantin Fedorovskiy, “Chui's conjecture in Bergman spaces”, arXiv:2009.01898 (2020).

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