Outer-function characterization in the upper half-plane

Let (G,θ)(G,\theta) be a compactification, let hHp(G,θ)h\in H^p(G,\theta) be a continuous function with bounded spectrum contained in [0,)[0,\infty), and let f=hθf=h\circ\theta. Then ff extends to an entire function FF bounded in the upper half-plane. The function hh is outer when it satisfies the outer-function integral condition

Glogh=logGh.\int_G\log|h|=\log\left|\int_Gh\right|.

Outer-function characterization. The function hh above is outer if and only if FF has no zeros in the open upper half-plane.

This connects Hardy-space factorization on the compactification with zero-freeness of the associated entire function. The excerpt presents the assertion without indicating whether it is proved or remains open.

Sources & referencesView supporting material

Primary source

Wayne Lawton, “Distribution of Small Values of Bohr Almost Periodic Functions with Bounded Spectrum”, arXiv:1904.09373 (2019).

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