On the Oberlin affine curvature condition

Abstract

We generalize the well-known notions of affine arclength and affine hypersurface measure to submanifolds of any dimension $d$ in ${\mathbb{R}}^n$, $1\le d\le n-1$. We show that a canonical equiaffine-invariant measure exists and that, modulo sufficient regularity assumptions on the submanifold, the measure satisfies the affine curvature condition of Oberlin with an exponent which is best possible. The proof combines aspects of geometric invariant theory, convex geometry, and frame theory. A significant new element of the proof is a generalization to higher dimensions of an earlier result concerning inequalities of reverse Sobolev type for polynomials on arbitrary measurable subsets of the real line.