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Characterizations of Extremals for some Functionals on Convex Bodies


Published:20100706
Printed: Dec 2010
Christos Saroglou,
University of Crete, Department of Mathematics
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Abstract
We investigate equality cases in inequalities for Sylvestertype
functionals. Namely, it was proven by Campi, Colesanti, and Gronchi
that the quantity
$$
\int_{x_0\in K}\cdots\int_{x_n\in
K}[V(\textrm{conv}\{x_0,\dots,x_n\})]^pdx_0\cdots dx_n , n\geq d, p\geq
1
$$
is maximized by triangles among all planar convex bodies $K$
(parallelograms in the symmetric case). We show that these are the
only maximizers, a fact proven by Giannopoulos for $p=1$.
Moreover, if $h$: $\mathbb{R}_+\rightarrow \mathbb{R}_+$ is a
strictly increasing function and $W_j$ is the $j$th
quermassintegral in $\mathbb{R}^d$, we prove that the functional
$$
\int_{x_0\in K_0}\cdots\int_{x_n\in
K_n}h(W_j(\textrm{conv}\{x_0,\dots,x_n\}))dx_0\cdots dx_n , n \geq d
$$
is
minimized among the $(n+1)$tuples of convex bodies of fixed
volumes if and only if $K_0,\dots,K_n$ are homothetic ellipsoids
when $j=0$ (extending a result of Groemer) and Euclidean balls
with the same center when $j>0$ (extending a result of Hartzoulaki
and Paouris).