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arXiv 2009.00474math.FA
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一般向量值数列空间的核嵌入及其在拟有界域上函数空间的Sobolev嵌入中的应用

Nuclear embeddings in general vector-valued sequence spaces with an application to Sobolev embeddings of function spaces on quasi-bounded domains

Dorothee D. Haroske, Hans-Gerd Leopold, Leszek Skrzypczak

摘要:

研究了定义在拟有界域$Ω\subset {\mathbb R}^d$上的Besov型和Triebel-Lizorkin型空间的核嵌入.定义在有界区域上的这种函数空间的对应问题已经被考虑了很长时间,直到最近才得到完整的答案。定义在拟有界域上的函数空间的紧嵌入已经被详细地研究过了,还涉及到它们的熵和$s$数。我们现在证明了在这方面的第一个和完全的核结果。核的概念早在1955年就由格罗滕迪克提出。我们的第二个主要贡献是推广著名的童结果(1969年)的特点核对角算子之间的数列空间的$\ell_r$型,$1\leq r\leq\infty$。我们现在可以将其扩展到具有$1\leq p,q\leq\infty$、$M_j\in {\mathbb N}_0$和具有$β_j>0$的权序列的$\ell_q(β_j \ell_p^{M_j})$类型的一般向量值数列空间的设置。特别是,我们证明了一个标准的嵌入$id_β: \ell_{q_1}(β_j \ell_{p_1}^{M_j}) \hookrightarrow \ell_{q_2}(\ell_{p_2}^{M_j})$是核。

英文摘要:

We study nuclear embeddings for spaces of Besov and Triebel-Lizorkin type defined on quasi-bounded domains $Ω\subset {\mathbb R}^d$. The counterpart for such function spaces defined on bounded domains has been considered for a long time and the complete answer was obtained only recently. Compact embeddings for function spaces defined on quasi-bounded domains have been studied in detail already, also concerning their entropy and $s$-numbers. We now prove the first and complete nuclearity result in this context. The concept of nuclearity has been introduce by Grothendieck in 1955 already. Our second main contribution is the generalisation of the famous Tong result (1969) which characterises nuclear diagonal operators acting between sequence spaces of $\ell_r$ type, $1\leq r\leq\infty$. We can now extend this to the setting of general vector-valued sequence spaces of type $\ell_q(β_j \ell_p^{M_j})$ with $1\leq p,q\leq\infty$, $M_j\in {\mathbb N}_0$ and weight sequences with $β_j>0$. In particular, we prove a criterion for the embedding $id_β: \ell_{q_1}(β_j \ell_{p_1}^{M_j}) \hookrightarrow \ell_{q_2}(\ell_{p_2}^{M_j})$ to be nuclear.

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