Density of Neumann regular smooth functions in Sobolev spaces of subanalytic manifolds

Fuente: arXiv
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Autor principal: Valette, Guillaume
Formato: Preprint
Publicado: 2026
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author Valette, Guillaume
author_facet Valette, Guillaume
contents We give characterizations of the bounded subanalytic $\mathscr{C}^\infty$ submanifolds $M$ of $\mathbb{R}^n$ for which the space of Neumann regular functions is dense in Sobolev spaces. By ``Neumann regular function'', we mean a function which is smooth at almost every boundary point and whose gradient is tangent to the boundary. In the case $p\in [1,2]$, we prove that the Neumann regular elements of $\mathscr{C}^\infty(\overline{M})$ are dense in $W^{1,p}(M)$ if and only if $M$ is connected at almost every boundary point. In the case $p$ large, we show that the Neumann regular Lipschitz elements of $\mathscr{C}^\infty(M)$ are dense in $W^{1,p}(M)$ if and only if $M$ is connected at every boundary point. The proof involves the construction of Lipschitz Neumann regular partitions of unity, which is of independent interest.
format Preprint
id arxiv_https___arxiv_org_abs_2602_12007
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Density of Neumann regular smooth functions in Sobolev spaces of subanalytic manifolds
Valette, Guillaume
Analysis of PDEs
46B35, 35A21, 32B20, 14P10
We give characterizations of the bounded subanalytic $\mathscr{C}^\infty$ submanifolds $M$ of $\mathbb{R}^n$ for which the space of Neumann regular functions is dense in Sobolev spaces. By ``Neumann regular function'', we mean a function which is smooth at almost every boundary point and whose gradient is tangent to the boundary. In the case $p\in [1,2]$, we prove that the Neumann regular elements of $\mathscr{C}^\infty(\overline{M})$ are dense in $W^{1,p}(M)$ if and only if $M$ is connected at almost every boundary point. In the case $p$ large, we show that the Neumann regular Lipschitz elements of $\mathscr{C}^\infty(M)$ are dense in $W^{1,p}(M)$ if and only if $M$ is connected at every boundary point. The proof involves the construction of Lipschitz Neumann regular partitions of unity, which is of independent interest.
title Density of Neumann regular smooth functions in Sobolev spaces of subanalytic manifolds
topic Analysis of PDEs
46B35, 35A21, 32B20, 14P10
url https://arxiv.org/abs/2602.12007