# A dual form of the sharp Nash inequality and its weighted generalization

## TL;DR

This paper introduces a dual form of the Nash inequality involving infimal convolution, providing explicit solutions and new weighted generalizations, along with their sharp constants.

## Contribution

It establishes a dual form of the Nash inequality with sharp constants and derives weighted generalizations through explicit computation and duality techniques.

## Key findings

- Derived a dual form of the Nash inequality with sharp constants.
- Solved explicitly the minimization problem for the infimal convolution.
- Established new weighted Nash inequalities and their duals.

## Abstract

The well known duality between the Sobolev inequality and the Hardy-Littlewood-Sobolev inequality suggests that the Nash inequality could also have an interesting dual form, even though the Nash inequality relates three norms instead of two. We provide such a dual form here with sharp constants. This dual inequality relates the $L^2$ norm to the infimal convolution of the $L^\infty $ and $H^{-1}$ norms. The computation of this infimal convolution is a minimization problem, which we solve explicitly, thus providing a new proof of the sharp Nash inequality itself. This proof, via duality, also yields the sharp form of some new, weighted generalizations of the Nash inequality as well as the dual of these weighted variants.