A Sharp Surface-Area Extension of Vaaler's Theorem

Abstract

Karasev proved, in dimensions two and three, a sharp surface-area counterpart of a polyhedral extension of Vaaler's theorem [8, Theorem 1.2]. We remove the dimension restriction. More precisely, if an $n$-dimensional convex polytope $P$ contains the origin in its interior and the affine hull of every nonempty proper face of codimension $k\in \{1,\dots ,n\}$ is at distance at least $\sqrt{k}$ from the origin, then $${\mathcal{H}}^{n-1}(\partial P)⩾n{2}^n.$$ Consequently, the boundary of every $n$-dimensional linear section of the cube $[-1,1{]}^N$ has $(n-1)$-dimensional measure at least $n{2}^n$. This confirms, in all dimensions, a conjecture of Grigory M. Ivanov recorded by Karasev [8, Section 1]. The proof combines the Rogers--Karasev flag decomposition with a dimension-free Gaussian comparison for orthoschemes. Its main step is an ordered-square substitution which converts all face-distance assumptions into a pointwise domination of a single positive integral. We also disprove the naive extension to all skeletal measures, formulate a ridge-skeleton conjecture, and establish two partial results toward it.

arXiv comment12 pages