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The Multifractal Spectra of V-Statistics

Let $(X, T)$ be a topological dynamical system and let $Φ: X^r \to \mathbb{R}$ 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 $Φ$ 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 $Φ$ is Hölder continuous, the spectrum of the limit of higher order V-statistics ($r\ge 2$) may be discontinuous even for very nice kernel $Φ$.