Constrained convex bodies with extremal affine surface areas

TL;DR

This paper introduces extremal affine surface areas for convex bodies, providing asymptotic estimates and revealing their proportionality to volume powers, with connections to lattice polytopes and geometric bounds.

Contribution

It defines and analyzes extremal inner and outer affine surface areas, deriving asymptotic estimates and exploring their geometric properties in higher dimensions.

Findings

Both extremal affine surface areas are proportional to a power of volume.

Asymptotic estimates are obtained using thin shell bounds and L"owner ellipsoids.

Results extend understanding of affine surface areas beyond known 2D cases.

Abstract

Given a convex body K in R^n and p in R, we introduce and study the extremal inner and outer affine surface areas IS_p(K) = sup_{K'\subseteq K} (as_p(K') ) and os_p(K)=inf_{K'\supseteq K} (as_p(K') ), where as_p(K') denotes the L_p-affine surface area of K', and the supremum is taken over all convex subsets of K and the infimum over all convex compact subsets containing K. The convex body that realizes IS_1(K) in dimension 2 was determined by Barany. He also showed that this body is the limit shape of lattice polytopes in K. In higher dimensions no results are known about the extremal bodies. We use a thin shell estimate of Guedon and Milman and the L\"owner ellipsoid to give asymptotic estimates on the size of IS_p(K) and os_p(K). Surprisingly, both quantities are proportional to a power of volume.