The Multifractal Spectra of V-Statistics

Abstract

Let $(X,T)$ be a topological dynamical system and let $\Phi :X^r\to \mathbb{R}$ be a continuous function on the product space $X^r=X\times ...\times X$ ($r\ge 1$). We are interested in the limit of V-statistics taking $\Phi$ as kernel: [\lim_{n\to \infty} n^{-r}\sum_{1\le i_1, ..., i_r\le n} Φ(T^{i_1}x, ..., T^{i_r} x).] The multifractal spectrum of topological entropy of the above limit is expressed by a variational principle when the system satisfies the specification property. Unlike the classical case ($r=1$) where the spectrum is an analytic function when $\Phi$ is Hölder continuous, the spectrum of the limit of higher order V-statistics ($r\ge 2$) may be discontinuous even for very nice kernel $\Phi$.

15 pages; minor revision after the referee report; to appear in Proceedings of the Conference on Fractals and Related Fields II (Porquerolles, June 2011)