Weak mixing sequence conjecture for functions satisfying the correlation condition

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Let (X,B,μ,T)(X,\mathscr{B},\mu,T) be a measure-preserving system, let UU denote its Koopman operator, and let f∈L2(X,μ)f\in L^2(X,\mu) satisfy

lim⁡N→∞1N∑n=1N∣⟨Unf,g⟩∣=0\lim_{N\rightarrow\infty}\frac{1}{N}\sum_{n=1}^N\left|\langle U^n f,g\rangle\right|=0

for every g∈L2(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 x∈Xx\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.

References

Primary source

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

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