Stone-Weierstrass theorem for homogeneous polynomials and its role in convex geometry

Abstract

We give a uniform approximation of the characteristic function of the boundary of a centrally symmetric n-dimensional compact and convex set by homogeneous polynomials of even degree $d$ fulfilling $|g_d-1|\leq E/d^{1/2-\beta}$, for every $\beta>0$, large enough $d$, and some constant $E$ only depending on $n$ and $K$. In particular, this proves a conjecture posed by Kroo in 2004, also known as the Stone-Weierstrass theorem for homogeneous polynomials. Moreover, we introduce the d-volume ratio for a convex body $K$ in $\mathbb R^n$, by means of its d-Lasserre-L\"owner polynomial. We also prove an upper bound of the d-volume ratio of the form $1+F/d^{3/2-\beta}$, for every $\beta>0$, large enough $d$, and $F$ some constant only depending on $n$.