$\Phi$-inequalities on domains

D. Stolyarov

Zapiski Nauchnykh Seminarov POMI, Investigations on linear operators and function theory. Part 52, Tome 537 (2024), pp. 128-150

Résumé

We find necessary and sufficient conditions on the function $\Phi$ for the inequality $$ \Big|\int_\Omega \Phi(K*f)\Big|\lesssim \|f\|_{L_1(\mathbb{R}^d)}^p $$ to be true. Here $K$ is a (possibly vector valued) kernel positive homogeneous of degree $\alpha - d$, $\Phi$ is a $p$-homogeneous function, and $p=d/(d-\alpha)$. The domain $\Omega\subset \mathbb{R}^d$ is either bounded with $C^{1,\beta}$ smooth boundary for some $\beta > 0$ or a halfspace in $\mathbb{R}^d$. As a corollary, we describe the functions $\Phi\colon \mathbb{R}^d \to \mathbb{R}$ positive homogeneous of order $d/(d-1)$ that are suitable for the bound $$ \Big|\int_\Omega \Phi(\nabla u)\Big|\lesssim \int_\Omega |\Delta u|. $$