Semirandom pointwise averaging conjecture

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Let (un)n≥1(\mathbb u_n)_{n\geq 1} be a decreasing sequence of probabilities, and let δ>0\delta>0. Suppose

un⋅n(log⁡log⁡n)1+δ→∞\mathbb u_n\cdot \frac{n}{(\log\log n)^{1+\delta}}\to\infty

and

un→0.\mathbb u_n\to 0.

Semirandom pointwise averaging conjecture. Then the random sequence Rω={r1<r2<r3<… }R^\omega=\{r_1<r_2<r_3<\dots\} satisfies, in every dynamical system, for bounded functions FiF_i,

lim⁡N→∞1N∑n<NTnF1(x)TrnF2(x)=F‾1 F‾2\lim_{N\to\infty}\frac1N\sum_{n<N}T^nF_1(x)T^{r_n}F_2(x)=\overline F_1\,\overline F_2

for almost every x∈Xx\in X, where F‾i\overline F_i is the projection of FiF_i to the TT-invariant functions.

The supplied context gives a related theorem with the stronger condition involving n1/2/log⁡3+δnn^{1/2}/\log^{3+\delta}n, and explains that the zero-density assumption is necessary for the stated limit. The conjectural statement's resolution is not supplied here.

References

Primary source

Nikos Frantzikinakis, Emmanuel Lesigne and Máté Wierdl, “Random differences in Szemerédi's theorem and related results”, arXiv:1307.1922 (2014).

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