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arXiv · 2608.30212

A Painlevé equation for the Hörmander-Bernhardsson constant

Friedrich Littmann
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Abstract

The Hörmander-Bernhardsson constant $\mathscr{C}$ is the sharp constant in $|f(0)|\le \mathscr{C} \|f\|_1$ for entire functions of exponential type $\le π$. We prove that $\mathscr{C} = 2πθ_*^{-2}$ where $θ_*$ is the least positive singularity of the regular solution $v$ with $v(0)=0$ of the cosh-Gordon equation $v_{θθ} + v_θ/θ= \cosh(v)$. It is known that $\mathscr{C}$ is a scaling limit in $n$ from the analogous problem for polynomials of degree $\le n$. We reformulate the polynomial problem as a Padé approximation problem at infinity. The associated matrix Riemann-Hilbert problem is analyzed by a Deift-Zhou steepest descent whose local parametrix is built from a Painlevé transcendent.

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Friedrich Littmann. 2026-09-17. A Painlevé equation for the Hörmander-Bernhardsson constant. https://arxiv.org/abs/2608.30212

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