The positive-characteristic intersection-of-orbits conjecture for polynomials

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Let KK be a field of characteristic pp, and let f,g∈K[x]f,g\in K[x] be polynomials of degrees larger than 11. Suppose that there exist α,β∈K\alpha,\beta\in K such that Of(α)∩Og(β)\mathcal{O}_f(\alpha)\cap\mathcal{O}_g(\beta) is infinite. A polynomial is additive if it satisfies h(x+y)=h(x)+h(y)h(x+y)=h(x)+h(y), and a polynomial is linearly conjugate to hh if it has the form λ−1∘h∘λ\lambda^{-1}\circ h\circ\lambda for a linear polynomial λ\lambda.

Intersection-of-orbits conjecture. At least one of the following holds: (1) there exist m,n∈Nm,n\in{\mathbb N} such that fm=gnf^m=g^n; or (2) there exist linear polynomials λ,μ∈K‾[x]\lambda,\mu\in\overline{K}[x] and additive polynomials f~,g~∈K‾[x]\widetilde f,\widetilde g\in\overline{K}[x] such that

f=λ−1∘f~∘λ,g=μ−1∘g~∘μ,f=\lambda^{-1}\circ\widetilde f\circ\lambda,\qquad g=\mu^{-1}\circ\widetilde g\circ\mu,

and there exists m∈Nm\in{\mathbb N} such that

f~m∘g~m=g~m∘f~m.\widetilde f^m\circ\widetilde g^m=\widetilde g^m\circ\widetilde f^m.

This conjecture modifies the common-iterate conclusion known over characteristic zero to account for positive-characteristic counterexamples involving additive polynomials. Its full generality remains open, and no counterexamples are known.

References

Primary source

Simone Coccia, Dragos Ghioca, Jungin Lee and Gyeonghyeon Nam, “Intersection of orbits for polynomials in characteristic p”, arXiv:2408.06937 (2024).

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