The colliding orbits conjecture for non-additive polynomials

From papers

Let LL be a field of characteristic p>0p>0, let α1,α2,βL\alpha_1,\alpha_2,\beta\in L, and let fFp[x]f\in\overline{\mathbb{F}}_p[x] be a polynomial of degree d2d\geq 2 that is not additive. Assume that not all of α1\alpha_1, α2\alpha_2, and β\beta belong to Fp\overline{\mathbb{F}}_p. Define

Cf(α1,α2;β):={λL: there are m,nN such that fλm(α1)=fλn(α2)=β}.C_f(\alpha_1,\alpha_2;\beta):=\{\lambda\in\overline{L}:\text{ there are }m,n\in\mathbb{N}\text{ such that }f_\lambda^m(\alpha_1)=f_\lambda^n(\alpha_2)=\beta\}.

The colliding orbits conjecture. The set Cf(α1,α2;β)C_f(\alpha_1,\alpha_2;\beta) is infinite if and only if f(α1)=f(α2)f(\alpha_1)=f(\alpha_2). This problem concerns when the strict forward orbits of two points under the family fλf_\lambda both contain a target point for infinitely many parameters. The monomial case f(x)=xdf(x)=x^d with d2d\geq 2 was settled, while the stated general case is presented as a conjecture.

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Sources & referencesView supporting material

Primary source

Jungin Lee and GyeongHyeon Nam, “On simultaneously preperiodic points for one-parameter families of polynomials in characteristic p”, arXiv:2509.15079 (2025).

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