A remark on projection outer volume ratio

Abstract

We study the projection outer volume ratio ${\mathrm{povr}}_k(K)$ introduced by D. Galicer, A.E. Litvak, M. Merzbacher, and D. Pinasco. When $k\le n/2$, we provide sharp bounds in the general case, namely \[ {\rm povr}_k(K)\leq C \max\Big\{1, \sqrt{\frac{k}{\ln(2n/k)}}\Big\}, \] where the maximal order is obtained for $K=B_1^n$. Moreover, in the important particular case $K=B_2^n$ we show that ${\mathrm{povr}}_k(B_2^n)$ is bounded by an absolute constant whenever $k\le n/2$ and \[ {\rm povr}_k(B_2^n)\leq C\sqrt{\frac{n}{n-k}}\, \ln\left(1+\frac{n}{n-k}\right) \] for $k>n/2$. The latter bound is sharp up to a logarithmic term.