Contractive Riesz projection conjecture and its endpoint logarithmic inequality

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Let PP denote the Riesz projection from L2(T)L^2(\mathbb{T}) onto H2H^2, and let rr and qq satisfy

1<r≤∞,q=4(1−1r).1<r\leq\infty,\qquad q=4\left(1-\frac{1}{r}\right).

Riesz projection contractivity conjecture. The operator PP is a contraction from Lr(T)L^r(\mathbb{T}) to HqH^q. In addition, for every f∈L1(T)f\in L^1(\mathbb{T}),

exp⁡(∫02πlog⁡∣Pf(eiθ)∣ dθ2π)≤∥f∥L1.\exp\left(\int_0^{2\pi}\log|Pf(e^{i\theta})|\,\frac{d\theta}{2\pi}\right)\leq\|f\|_{L^1}.

This conjecture connects the coefficient inequalities with contractive bounds for the Riesz projection. The source notes the endpoint L∞(T)→H4L^\infty(\mathbb{T})\to H^4 result and its sharpness, but does not resolve the full asserted family or the accompanying L1L^1 inequality.

References

Primary source

Ole Fredrik Brevig, Joaquim Ortega-Cerdà, Kristian Seip and Jing Zhao, “Contractive inequalities for Hardy spaces”, arXiv:1706.00738 (2018).

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