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} \Phi(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 H\"{o}lder continuous, the spectrum of the limit of higher order V-statistics ($r\ge 2$) may be discontinuous even for very nice kernel $\Phi$.