A complete answer to the strong density problem in Sobolev spaces with values into compact manifolds

Fuente: arXiv
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Autore principale: Detaille, Antoine
Natura: Preprint
Pubblicazione: 2023
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author Detaille, Antoine
author_facet Detaille, Antoine
contents We consider the problem of strong density of smooth maps in the Sobolev space $ W^{s,p}(Q^{m};\mathcal{N}) $, where $ 0 < s < +\infty $, $ 1 \leq p < +\infty $, $ Q^{m} $ is the unit cube in $ \mathbb{R}^{m} $, and $ \mathcal{N} $ is a smooth compact connected Riemannian manifold without boundary. Our main result fully answers the strong density problem in the whole range $ 0 < s < +\infty $: the space $ \mathcal{C}^{\infty}(\overline{Q}^{m};\mathcal{N}) $ is dense in $ W^{s,p}(Q^{m};\mathcal{N}) $ if and only if $ π_{[sp]}(\mathcal{N}) = \{0\} $. This completes the results of Bethuel ($ s=1 $), Brezis and Mironescu ($ 0 < s < 1 $), and Bousquet, Ponce, and Van Schaftingen ($ s = 2 $, $ 3 $, ...). We also consider the case of more general domains $ Ω$, in the setting studied by Hang and Lin when $ s = 1 $.
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publishDate 2023
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spellingShingle A complete answer to the strong density problem in Sobolev spaces with values into compact manifolds
Detaille, Antoine
Functional Analysis
46E35
We consider the problem of strong density of smooth maps in the Sobolev space $ W^{s,p}(Q^{m};\mathcal{N}) $, where $ 0 < s < +\infty $, $ 1 \leq p < +\infty $, $ Q^{m} $ is the unit cube in $ \mathbb{R}^{m} $, and $ \mathcal{N} $ is a smooth compact connected Riemannian manifold without boundary. Our main result fully answers the strong density problem in the whole range $ 0 < s < +\infty $: the space $ \mathcal{C}^{\infty}(\overline{Q}^{m};\mathcal{N}) $ is dense in $ W^{s,p}(Q^{m};\mathcal{N}) $ if and only if $ π_{[sp]}(\mathcal{N}) = \{0\} $. This completes the results of Bethuel ($ s=1 $), Brezis and Mironescu ($ 0 < s < 1 $), and Bousquet, Ponce, and Van Schaftingen ($ s = 2 $, $ 3 $, ...). We also consider the case of more general domains $ Ω$, in the setting studied by Hang and Lin when $ s = 1 $.
title A complete answer to the strong density problem in Sobolev spaces with values into compact manifolds
topic Functional Analysis
46E35
url https://arxiv.org/abs/2305.12589