# Bounds for radii of starlikeness of some $q$-Bessel functions

## TL;DR

This paper establishes tight bounds for the radii of starlikeness of certain $q$-Bessel functions using Euler-Rayleigh inequalities, and explores the role of the Laguerre-Pólya class in deriving these bounds.

## Contribution

It provides new bounds for the radii of starlikeness of $q$-Bessel functions and introduces three different normalizations for each, utilizing properties of the Laguerre-Pólya class.

## Key findings

- Derived tight bounds for the radii of starlikeness of $q$-Bessel functions.
- Applied Euler-Rayleigh inequalities to estimate zeros of these functions.
- Obtained new bounds for the first positive zero of the derivative of classical Bessel functions.

## Abstract

In this paper the radii of starlikeness of the Jackson and Hahn-Exton $q$-Bessel functions are considered and for each of them three different normalization are applied. By applying Euler-Rayleigh inequalities for the first positive zeros of these functions tight lower and upper bounds for the radii of starlikeness of these functions are obtained. The Laguerre-P\'olya class of real entire functions plays an important role in this study. In particular, we obtain some new bounds for the first positive zero of the derivative of the classical Bessel function of the first kind.