Random section and random simplex inequality

A. E. Litvak ; D. N. Zaporozhets

Zapiski Nauchnykh Seminarov POMI, Probability and statistics. Part 31, Tome 505 (2021), pp. 162-171

Résumé

Consider some convex body $K\subset\mathbb R^d$. Let $X_1,\dots, X_k$, where $k\leq d$, 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 $p\geq -d+k+1$, $$ \mathbf E |K\cap\xi_k|^{d+p}\leq c_{d,k,p}\cdot|K|^k \mathbf E |\mathrm{conv}(0,X_1,\dots,X_k)|^p, $$ 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 if this inequality which similarly generalizes the Schneider inequality and the Blaschke-Grömer inequality.