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Concentration of mass and central limit properties of isotropic convex bodies
Authors:G. Paouris
Affiliation:Department of Mathematics, University of Crete, Iraklion 714-09, Greece
Abstract:We discuss the following question: Do there exist an absolute constant $c>0$ and a sequence $phi (n)$ tending to infinity with $n$, such that for every isotropic convex body $K$ in ${mathbb R}^n$ and every $tgeq 1$the inequality ${rm Prob}left (big { xin K:Vert xVert _2geq csqrt{n}L_Ktbig }right ) leqexp big (-phi (n)tbig )$ holds true? Under the additional assumption that $K$ is 1-unconditional, Bobkov and Nazarov have proved that this is true with $phi (n)simeqsqrt{n}$. The question is related to the central limit properties of isotropic convex bodies. Consider the spherical average $f_K(t)=int_{S^{n-1}}vert Kcap (theta^{perp }+ttheta )vertsigma (dtheta )$. We prove that for every $gammageq 1$ and every isotropic convex body $K$in ${mathbb R}^n$, the statements (A) ``for every $tgeq 1$, ${rm Prob}left (big{ xin K:Vert xVert _2geq gammasqrt{n}L_Ktbig}right )leqexp big (-phi (n)tbig )$" and (B) ``for every $0<t leq c_1(gamma )sqrt{phi (n)}L_K$, $f_K(t)leq frac{c_2}{L_K}exp big (-t^2/(c_3(gamma )^2L_K^2)big )$, where $c_i(gamma )simeqgamma $" are equivalent.

Keywords:Isotropic convex bodies   concentration of volume   central limit theorem
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