Weak mixing sequence conjecture for functions satisfying the correlation condition

Let (X,B,μ,T)(X,\mathscr{B},\mu,T) be a measure-preserving system, let UU denote its Koopman operator, and let fL2(X,μ)f\in L^2(X,\mu) satisfy

limN1Nn=1NUnf,g=0\lim_{N\rightarrow\infty}\frac{1}{N}\sum_{n=1}^N\left|\langle U^n f,g\rangle\right|=0

for every gL2(X,μ)g\in L^2(X,\mu). A sequence (zn)n=1(z_n)_{n=1}^{\infty} is weakly mixing if its correlations have the corresponding Cesàro convergence to zero. The weak mixing sequence conjecture. Under these assumptions, for almost every xXx\in X, the sequence (f(Tnx))n=1(f(T^n x))_{n=1}^{\infty} is weakly mixing. The conjecture asks whether the stated Hilbert-space correlation condition on ff suffices for almost-everywhere weak mixing of its pointwise orbit sequence; the surrounding discussion explains that this would remove the need for the underlying system to be weakly mixing in the relevant pointwise ergodic theorem.

Sources & referencesView supporting material

Primary source

Sohail Farhangi, “Pointwise Ergodic Theorems for Higher Levels of Mixing”, arXiv:2107.07861 (2021).

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