Improved Poincar\'e inequalities

TL;DR

This paper demonstrates that the Gaussian Poincaré inequality can be improved by adding positive terms, with optimal constants identified through a recursive method, extending the concept of inequality improvement beyond Hardy inequalities.

Contribution

It introduces a recursive approach to improve the Gaussian Poincaré inequality and related Hardy-Poincaré inequalities, providing asymptotic expansions with optimal constants.

Findings

Improved Gaussian Poincaré inequality with positive additive terms

Recursive method for identifying optimal constants

Extension to Hardy-Poincaré inequalities interpolating between Hardy and Gaussian cases

Abstract

Although the Hardy inequality corresponding to one quadratic singularity, with optimal constant, does not admit any extremal function, it is well known that such a potential can be improved, in the sense that a positive term can be added to the quadratic singularity without violating the inequality, and even a whole asymptotic expansion can be build, with optimal constants for each term. This phenomenon has not been much studied for other inequalities. Our purpose is to prove that it also holds for the gaussian Poincar\'e inequality. The method is based on a recursion formula, which allows to identify the optimal constants in the asymptotic expansion, order by order. We also apply the same strategy to a family of Hardy-Poincar\'e inequalities which interpolate between Hardy and gaussian Poincar\'e inequalities.