Liu–Ponnusamy conjectures on Bohr radii for harmonic quasi-subordination

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Let D\mathbb D be the unit disk. Suppose that

f(z)=h(z)+g(z)‾=∑n=0∞anzn+∑n=2∞bnzn‾f(z)=h(z)+\overline{g(z)}=\sum_{n=0}^{\infty}a_nz^n+\overline{\sum_{n=2}^{\infty}b_nz^n}

is a sense-preserving harmonic mapping in D\mathbb D and h≺φh\prec\varphi.

Liu–Ponnusamy's conjectures. (a) If φ\varphi is univalent and convex in D\mathbb D, then

∑n=1∞∣an∣rn+∑n=2∞∣bn∣rn≤dist⁡(φ(0),∂φ(D))\sum_{n=1}^{\infty}|a_n|r^n+\sum_{n=2}^{\infty}|b_n|r^n\leq \operatorname{dist}(\varphi(0),\partial\varphi(\mathbb D))

for ∣z∣=r≤ρc=0.299823⋯|z|=r\leq\rho_c=0.299823\cdots, where ρc\rho_c is the positive root of

4r1−r+2ln⁡(1−r)=1.\frac{4r}{1-r}+2\ln(1-r)=1.

(b) If φ\varphi is univalent in D\mathbb D, then the inequality in (a) holds for ∣z∣=r≤ρs=0.161353⋯|z|=r\leq\rho_s=0.161353\cdots, where ρs\rho_s is the positive real root of

2r2(1−r)2−ln⁡(1−r)=14.\frac{2r^2}{(1-r)^2}-\ln(1-r)=\frac14.

These conjectures concern sharp Bohr-type radii for sense-preserving harmonic mappings, extending the corresponding finite-distortion results to the limiting case K→∞K\to\infty; their resolution is not established in the supplied text.

References

Primary source

Ming-Sheng Liu, Saminathan Ponnusamy and Jun Wang, “Bohr's phenomenon for the classes of Quasi-subordination and K-quasiregular harmonic mappings”, arXiv:2004.08903 (2020).

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