The centralizer index conjecture for rational maps with automorphisms

Let KK be a field, let ϕK(x)\phi\in K(x), and let TT_\infty be its pre-image tree rooted at 00. Let A(ϕ)A(\phi) be the subgroup of Aut(T)\operatorname{Aut}(T_\infty) generated by the actions of all nontrivial Möbius transformations mPGL2(K)m\in\operatorname{PGL}_2(K) satisfying m1ϕm=ϕm^{-1}\circ\phi\circ m=\phi and m(0)=0m(0)=0. Let C(ϕ)C(\phi) be the centralizer of A(ϕ)A(\phi) in Aut(T)\operatorname{Aut}(T_\infty). Centralizer index conjecture. If A(ϕ)A(\phi) is nontrivial, then

[Aut(T):C(ϕ)]=.[\operatorname{Aut}(T_\infty):C(\phi)]=\infty.

The centralizer contains the arboreal Galois group because the Galois action commutes with the KK-defined Möbius symmetries. The source gives no resolution of this conjecture.

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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