Generalized orthogonality of polynomial correlation sequences

Let kNk\in\mathbb{N}, let (X,μ,T)(X,\mu,T) be an invertible measure-preserving system, let P={p1,,pr}P=\{p_1,\ldots,p_r\} be a set of essentially distinct integral polynomials, let hh be an integral polynomial with hWP(P)h\notin \textup{\textsf{{WP}}}(P), and let αRQ\alpha\in\mathbb{R}\setminus\mathbb{Q}. If g:TCg:\mathbb{T}\to\mathbb{C} is Riemann integrable and f0,f1,,frL(μ)f_0,f_1,\ldots,f_r\in L^\infty(\mu), then

Generalized orthogonality conjecture.

limN1Nn=1N(g(h(n)α)Tgdλ)f0Tp1(n)f1Tpr(n)frdμ=0.\lim_{N\to\infty}\frac{1}{N}\sum_{n=1}^N\left(g(h(n)\alpha)-\int_{\mathbb{T}}g\,d\lambda\right)\int f_0T^{p_1(n)}f_1\cdots T^{p_r(n)}f_r\,d\mu=0.

The conjecture seeks to extend the Weyl-system orthogonality result to arbitrary invertible measure-preserving systems; the source notes technical complications in lifting the result to nilsystems. The source does not state whether it has been resolved.

Sources & referencesView supporting material

Primary source

Felipe Hernández, “Multiple Polynomial Recurrence in Weyl Systems”, arXiv:2504.19899 (2026).

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