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Rearrangement and polarization

By Gabriele Bianchi, Richard J. Gardner, Paolo Gronchi and Markus Kiderlen
CSGB Research Reports
No. 12, December 2019
Abstract:

The paper has two main goals. The first is to take a new approach to rearrangements on certain classes of measurable real-valued functions on $\mathbb{R}^n$. Rearrangements are maps that are monotonic (up to sets of measure zero) and equimeasurable, i.e., they preserve the measure of super-level sets of functions. All the principal known symmetrization processes for functions, such as Steiner and Schwarz symmetrization, are rearrangements, and these have a multitude of applications in diverse areas of the mathematical sciences. The second goal is to understand which properties of rearrangements characterize polarization, a special rearrangement that has proved particularly useful in a number of contexts. In order to achieve this, new results are obtained on the structure of measure-preserving maps on convex bodies and of rearrangements generally.

Keywords: Convex body, Steiner symmetrization, Schwarz symmetrization, Minkowski symmetrization, rearrangement, polarization

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