Pre-Schwarzian norm estimate for certain Ma-Minda Class of functions

TL;DR

This paper derives sharp bounds for the pre-Schwarzian norm of functions in certain Ma-Minda classes, specifically for classes defined by exponential and square root subordination functions.

Contribution

It provides the first sharp estimates of the pre-Schwarzian norm for functions in Ma-Minda classes with specific subordination functions.

Findings

Sharp pre-Schwarzian norm bounds for exponential case

Sharp pre-Schwarzian norm bounds for square root case

Results applicable to Alexander transformations of these classes

Abstract

Let $\mathcal{S}^*(\varphi)$ be the class of all analytic functions $f$ in the unit disk $\mathbb{D}=\{z\in\mathbb{C}:|z|<1\}$, normalized by $f(0)=f'(0)-1=0$ that satisfy the subordination relation $zf'(z)/f(z)\prec\varphi(z)$, where $\varphi$ is an analytic and univalent in $\mathbb{D}$ with ${\rm Re\,}\varphi(z)>0$ such that $\varphi(\mathbb{D})$ is symmetric with respect to the real axis and stralike with respect to $1$. In the present article, we obtain the sharp estimates of the pre-Schwarzian norm of $f$ and the Alexander transformation $J[f]$ for functions $f(z)$ in the class $\mathcal{S}^*(\varphi)$ when $\varphi(z)=e^{\lambda z}$, $0<\lambda\le\pi/2$ and $\varphi(z)=\sqrt{1+cz}$, $0<c\le1.$