### Mathematics Colloquium

** ALEXANDER VOLBERG
**

Michigan State University

**Title:**Non-homogeneous harmonic analysis, Geometric Measure Theory
and fine structures of harmonic measure

**Date:** Friday, October 19, 2018

**Place and Time:** Room 101, Love Building, 3:35-4:25 pm

**Refreshments:** Room 204, Love Building, 3:00 pm

**Abstract.**
One of the goals of harmonic analysis is to study singular
integrals. Singular integrals are ubiquitous objects and play an
important part in Geometric Measure Theory. The simplest ones are
called Calderon-Zygmund operators Their theory was completed in the
50's by Zygmund and Calderon. Or it seemed like that. The last 20
years saw the need to consider CZ operators in very bad environment,
so kernels are still very good, but the ambient set has no regularity
whatsoever.

Initially such situations appeared from the wish to solve some outstanding problems in complex analysis: such as problems of Painlev\'e, Ahlfors, Denjoy and Vitushkin.

The analysis of CZ operators on very bad sets and measures is also very fruitful in the part of Geometric Measure Theory that deals with rectifiability, and also helps a lot to understand the geometry of harmonic measure. Lennart Carleson, Nikolai Makarov, Jean Bourgain, Peter Jones and Tom Wolff obtained important results on metric properties of harmonic measure in the 80's and 90's. But most of the results concerned the structure of harmonic measure of planar domains. As an example of the use of non-homogeneous harmonic analysis, we will show how it allows us to understand very fine property of harmonic measure of any domain in any dimension and to find the answer to several problems of C Bishop dated from 1991.