Polynomial inequalities on the $\pi/4$-circle sector

TL;DR

This paper establishes sharp polynomial inequalities, including Bernstein and Markov inequalities, for 2-homogeneous polynomials on a sector of the complex plane, and computes related constants.

Contribution

It provides the first sharp Bernstein and Markov inequalities and calculates polarization and unconditional constants for polynomials on the $rac{ ext{ extpi}}{4}$-sector.

Findings

Sharp Bernstein inequalities derived

Sharp Markov inequalities established

Polarization and unconditional constants computed

Abstract

A number of sharp inequalities are proved for the space ${\mathcal P}\left(^2D\left(\frac{\pi}{4}\right)\right)$ of 2-homogeneous polynomials on ${\mathbb R}^2$ endowed with the supremum norm on the sector $D\left(\frac{\pi}{4}\right):=\left\{e^{i\theta}:\theta\in \left[0,\frac{\pi}{4}\right]\right\}$. Among the main results we can find sharp Bernstein and Markov inequalities and the calculation of the polarization constant and the unconditional constant of the canonical basis of the space ${\mathcal P}\left(^2D\left(\frac{\pi}{4}\right)\right)$.