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arXiv 2110.04072math.FA
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Banach 空间上有界算子代数之间的近似乘法映射

Approximately multiplicative maps between algebras of bounded operators on Banach spaces

Yemon Choi, Bence Horváth, Niels Jakob Laustsen

AI总结:

本文证明了可分自反 Banach 空间与一大类 Banach 空间的有界算子代数之间满足 AMNM 性质,并利用受上同调技术启发的新结果推广了 Johnson 的定理。

摘要:

我们证明,对于任意可分自反 Banach 空间 $X$ 以及一大类 Banach 空间 $E$(包括具有次对称收缩基的空间,以及所有 $1\leq p \leq \infty$ 的 $L_p$ 空间),每个近似乘法的有界线性映射 ${\mathcal B}(E)\to {\mathcal B}(X)$ 在算子范数下必然接近某个有界同态 ${\mathcal B}(E)\to {\mathcal B}(X)$。也就是说,$({\mathcal B}(E), {\mathcal B}(X))$ 具有 Johnson 意义下的 AMNM 性质(1988)。此前仅对 $1<p<\infty$ 的 $E=X=\ell_p$ 了解此结论;即便针对这些情形,我们也改进了先前方法并在各项估计中获得更好的常数。受上同调技术启发,一个新结果在我们的方法中发挥了关键作用,该结果确立了相对于顺从子代数的 AMNM 性质;这推广了 Johnson 的一个定理。

英文摘要:

We show that for any separable reflexive Banach space $X$ and a large class of Banach spaces $E$, including those with a subsymmetric shrinking basis but also all spaces $L_p$ for $1\leq p \leq \infty$, every bounded linear map ${\mathcal B}(E)\to {\mathcal B}(X)$ which is approximately multiplicative is necessarily close in the operator norm to some bounded homomorphism ${\mathcal B}(E)\to {\mathcal B}(X)$. That is, the pair $({\mathcal B}(E), {\mathcal B}(X))$ has the AMNM property in the sense of Johnson (\textit{J.~London Math.\ Soc.} 1988). Previously this was only known for $E=X=\ell_p$ with $1<p<\infty$; even for those cases, we improve on the previous methods and obtain better constants in various estimates. A crucial role in our approach is played by a new result, motivated by cohomological techniques, which establishes AMNM properties relative to an amenable subalgebra; this generalizes a theorem of Johnson (\textit{op cit.}).

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