English

Meromorphic functions with small Schwarzian derivative

Complex Variables 2017-09-05 v1

Abstract

We consider the family of all meromorphic functions ff of the form f(z)=1z+b0+b1z+b2z2+ f(z)=\frac{1}{z}+b_0+b_1z+b_2z^2+\cdots analytic and locally univalent in the puncture disk D0:={zC:0<z<1}\mathbb{D}_0:=\{z\in\mathbb{C}:\,0<|z|<1\}. Our first objective in this paper is to find a sufficient condition for ff to be meromorphically convex of order α\alpha, 0α<10\le \alpha<1, in terms of the fact that the absolute value of the well-known Schwarzian derivative Sf(z)S_f (z) of ff is bounded above by a smallest positive root of a non-linear equation. Secondly, we consider a family of functions gg of the form g(z)=z+a2z2+a3z3+g(z)=z+a_2z^2+a_3z^3+\cdots analytic and locally univalent in the open unit disk D:={zC:z<1}\mathbb{D}:=\{z\in\mathbb{C}:\,|z|<1\}, and show that gg is belonging to a family of functions convex in one direction if Sg(z)|S_g(z)| is bounded above by a small positive constant depending on the second coefficient a2a_2. In particular, we show that such functions gg are also contained in the starlike and close-to-convex family.

Keywords

Cite

@article{arxiv.1709.00529,
  title  = {Meromorphic functions with small Schwarzian derivative},
  author = {Vibhuti Arora and Swadesh Kumar Sahoo},
  journal= {arXiv preprint arXiv:1709.00529},
  year   = {2017}
}

Comments

16 pages. Submitted to a journal

R2 v1 2026-06-22T21:31:09.577Z