Random section and random simplex inequality

Abstract

Consider some convex body $K\subset {\mathbb{R}}^d$. Let $X_1,\dots ,X_k$, where $k\le d$, be random points independently and uniformly chosen in $K$, and let ${\xi }_k$ be a uniformly distributed random linear $k$-plane. We show that for $p\ge -d+k+1$, \[ \mathbb E\,|K\capξ_k|^{d+p}\leq c_{d,k,p} \cdot|K|^k\, \,\mathbb E\,|\mathrm{conv}(0,X_1, \dots,X_k)|^p, \] where $|\cdot |$ and $\mathrm{conv}$ denote the volume of correspondent dimension and the convex hull. The constant $c_{d,k,p}$ is such that for $k>1$ the equality holds if and only if $K$ is an ellipsoid centered at the origin, and for $k=1$ the inequality turns to equality. If $p=0$, then the inequality reduces to the Busemann intersection inequality, and if $k=d$ -- to the Busemann random simplex inequality. We also present an affine version of this inequality which similarly generalizes the Schneider inequality and the Blaschke-Grömer inequality.