Measures, annuli and dimensions

Abstract

Given a Radon probability measure $\mu$ supported in ${\mathbb{R}}^d$, we are interested in those points $x$ around which the measure is concentrated infinitely many times on thin annuli centered at $x$. Depending on the lower and upper dimension of $\mu$, the metric used in the space and the thinness of the annuli, we obtain results and examples when such points are of $\mu$-measure $0$ or of $\mu$-measure $1$. The measure concentration we study is related to ''bad points'' for the Poincaré recurrence theorem and to the first return times to shrinking balls under iteration generated by a weakly Markov dynamical system. The study of thin annuli and spherical averages is also important in many dimension-related problems, including Kakeya-type problems and Falconer's distance set conjecture.

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