Local avoidance conjecture for polynomial images of integers and primes

Let hZ[x]h\in\mathbb{Z}[x] be a nonzero polynomial, and let X=h(Z)X=h(\mathbb{Z}) or X=h(P)X=h(\mathcal{P}), where P\mathcal{P} denotes the set of primes. For each mNm\in\mathbb{N}, let XmX_m be the set of congruence classes modulo mm that intersect XX, and define

dX(m)=max{A:AZ/mZ, (AA)Xm=}.d_X(m)=\max\{|A|: A\subseteq\mathbb{Z}/m\mathbb{Z},\ (A-A)\cap X_m=\emptyset\}.

Here μ(X)\mu(X) denotes the maximal density of an XX-set, namely a set whose pairwise differences avoid XX. Local avoidance conjecture. For every such hh and XX, we have

μ(X)=supmNdX(m)m.\mu(X)=\sup_{m\in\mathbb{N}}\frac{d_X(m)}{m}.

The conjecture asserts that for polynomial images of the integers and primes, the maximal global density of a set avoiding XX-differences is determined by the strongest finite-modulus local avoidance obstruction. It extends the principle that local obstructions are the only obstructions in intersectivity questions; the supplied context does not state whether it is known or open.

Sources & referencesView supporting material

Primary source

Christian Dean, Haley Havard, Elizabeth Hawkins, Patch Heard, Andrew Lott and Alex Rice, “Notes and computations on forbidden differences”, arXiv:2508.03650 (2025).

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