A Characterization of $α$-Convex Functions with Sharp Coefficient and Schwarzian Estimates

Abstract

The class $M_α$ of $α$-convex functions, introduced by Mocanu in 1969, interpolates between starlike and convex functions. We prove a characterization of $M_α$ that extends a theorem of Chuaqui, Duren, and Osgood from the convex case to the full class, and determine sharp values of $β$ for which $M_α\subset C_β$ and $C_β\subset M_α$. We also obtain a sharp Fekete--Szegő inequality, bounds for the order and the Schwarzian norm, and an explicit formula for the Schwarzian norm of the $α$-Koebe function for $α= 1/n$, $n \in \mathbb{N}$, which we verify for $n \leq 9$ and conjecture to hold in general.