On the Comparison of Measures of Convex Bodies via Projections and Sections

Abstract

In this manuscript, we study the inequalities between measures of convex bodies implied by comparison of their projections and sections. Recently, Giannopoulos and Koldobsky proved that if convex bodies $K,L$ satisfy $|K|{\theta }^{\perp }|\le |L\cap {\theta }^{\perp }|$ for all $\theta \in S^{n-1}$, then $|K|\le |L|$. Firstly, we study the reverse question: in particular, we show that if $K,L$ are origin-symmetric convex bodies in John's position with $|K\cap {\theta }^{\perp }|\le |L|{\theta }^{\perp }|$ for all $\theta \in S^{n-1}$ then $|K|\le \sqrt{n}|L|$. The condition we consider is weaker than both the conditions $|K\cap {\theta }^{\perp }|\le |L\cap {\theta }^{\perp }|$ and $|K|{\theta }^{\perp }|\le |L|{\theta }^{\perp }|$ for all $\theta \in S^{n-1}$ that appear in the Busemann-Petty and Shephard problems respectively. Secondly, we appropriately extend the result of Giannopoulos and Koldobsky to various classes of measures possessing concavity properties, including log-concave measures.

26 pages