English

Bohr phenomenon for certain classes of harmonic mappings

Complex Variables 2021-04-07 v1

Abstract

Bohr phenomenon for analytic functions f f where f(z)=n=0anzn f(z)=\sum_{n=0}^{\infty}a_nz^n , first introduced by Harald Bohr in 1914 1914 , deals with finding the largest radius rf r_f , 0<rf<1 0<r_f<1 , such that the inequality n=0anzn<1 \sum_{n=0}^{\infty}|a_nz^n|<1 holds whenever f(z)<1 |f(z)|<1 holds in the unit disk D={zC:z<1} \mathbb{D}=\{z\in\mathbb{C} : |z|<1\} . The Bohr phenomenon for the harmonic functions of the form f(z)=h+g f(z)=h+\overline{g} , where h(z)=n=0anzn h(z)=\sum_{n=0}^{\infty}a_nz^n and g(z)=n=1bnzn g(z)=\sum_{n=1}^{\infty}b_nz^n is to find the largest radius rf r_f , 0<rf<1 0<r_f<1 such that \begin{equation*} \sum_{n=1}^{\infty}\left(|a_n|+|b_n|\right)|z|^n\leq d(f(0),\partial f(\mathbb{D})) \end{equation*} holds for zrf |z|\leq r_f , where d(f(0),f(D)) d(f(0),\partial f(\mathbb{D})) is the Euclidean distance between f(0) f(0) and the boundary of f(D) f(\mathbb{D}) . In this paper, we prove several improved versions of the sharp Bohr radius for the classes of harmonic and univalent functions. Further, we prove several corollaries as a consequence of the main results.

Keywords

Cite

@article{arxiv.2104.02099,
  title  = {Bohr phenomenon for certain classes of harmonic mappings},
  author = {Molla Basir Ahamed and Vasudevarao Allu},
  journal= {arXiv preprint arXiv:2104.02099},
  year   = {2021}
}
R2 v1 2026-06-24T00:51:56.762Z