Abstract of a paper by Ohad Giladi, Manor Mendel, and Assaf Naor
This is an announcement for the paper "Improved bounds in the metric cotype inequality for Banach spaces" by Ohad Giladi, Manor Mendel, and Assaf Naor. Abstract: It is shown that if (X, ||.||_X) is a Banach space with Rademacher cotype q then for every integer n there exists an even integer m< n^{1+1/q}$ such that for every f:Z_m^n --> X we have \sum_{j=1}^n \Avg_x [ ||f(x+ (m/2) e_j)-f(x) ||_X^q ] < C m^q \Avg_{\e,x} [ ||f(x+\e)-f(x) ||_X^q ], where the expectations are with respect to uniformly chosen x\in Z_m^n and \e\in \{-1,0,1\}^n, and all the implied constants may depend only on q and the Rademacher cotype q constant of X. This improves the bound of m< n^{2+\frac{1}{q}} from [Mendel, Naor 2008]. The proof of the above inequality is based on a ``smoothing and approximation" procedure which simplifies the proof of the metric characterization of Rademacher cotype of [Mendel, Naor 2008]. We also show that any such ``smoothing and approximation" approach to metric cotype inequalities must require m> n^{(1/2)+(1/q)}. Archive classification: math.FA math.MG Mathematics Subject Classification: 46B80,46B85,51F99,05C12 Remarks: 27 pages, 1 figure The source file(s), cotypeGMN.bbl: 3212 bytes cotypeGMN.tex: 87911 bytes tr-jigsaw.eps: 52290 bytes tr-jigsaw.pdf: 28339 bytes, is(are) stored in gzipped form as 1003.0279.tar.gz with size 80kb. The corresponding postcript file has gzipped size 84kb. Submitted from: mendelma@gmail.com The paper may be downloaded from the archive by web browser from URL http://front.math.ucdavis.edu/1003.0279 or http://arXiv.org/abs/1003.0279 or by email in unzipped form by transmitting an empty message with subject line uget 1003.0279 or in gzipped form by using subject line get 1003.0279 to: math@arXiv.org.
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