The general symmetry conjecture for quadratic rational maps

Let KK be a global field of characteristic 00 or greater than 22, and let ϕ(x)K(x)\phi(x)\in K(x) have degree 22. Assume that ϕ\phi is not post-critically finite and that 00 is not periodic under ϕ\phi. Let TT_\infty be the pre-image tree rooted at 00, let G(ϕ)G_\infty(\phi) be its arboreal Galois group, and let C(ϕ)C(\phi) be the centralizer of the subgroup generated by Möbius symmetries commuting with ϕ\phi and fixing 00. General symmetry conjecture. If ϕ\phi commutes with a nontrivial Möbius transformation fixing 00, then

[C(ϕ):G(ϕ)]<.[C(\phi):G_\infty(\phi)]<\infty.

Every degree-two rational map commuting with a nontrivial Möbius transformation is conjugate to the displayed family, so this conjecture generalizes the corresponding case over Q\mathbb{Q}. The source presents it as equivalent to the family conjecture over Q\mathbb{Q} and gives no resolution.

Sources & referencesView supporting material

Primary source

Rafe Jones, “Galois representations from pre-image trees: an arboreal survey”, arXiv:1402.6018 (2014).

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