Outer-function characterization in the upper half-plane

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Let (G,θ)(G,\theta) be a compactification, let h∈Hp(G,θ)h\in H^p(G,\theta) be a continuous function with bounded spectrum contained in [0,∞)[0,\infty), and let f=h∘θf=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

∫Glog⁡∣h∣=log⁡∣∫Gh∣.\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.

References

Primary source

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

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