Jones's index conjecture for quadratic rational maps

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Let KK be a global field, let f∈K(x)f\in K(x) have degree two, and let T∞T_\infty be the infinite rooted binary tree of preimages of a root α\alpha under ff. Write G∞(f,α)G_\infty(f,\alpha) for the image of the associated arboreal Galois representation. Jones's conjecture. One has

[Aut⁡(T∞):G∞(f,α)]=∞[\operatorname{Aut}(T_\infty):G_\infty(f,\alpha)]=\infty

if and only if at least one of the following holds: ff is postcritically finite; the two critical points γ1\gamma_1 and γ2\gamma_2 satisfy fr+1(γ1)=fr+1(γ2)f^{r+1}(\gamma_1)=f^{r+1}(\gamma_2) for some r≥1r\geq 1; the root α\alpha is periodic under ff; or a nontrivial Möbius transformation commuting with ff fixes α\alpha. This gives criteria for when the arboreal image has infinite index in the full automorphism group; the supplied text does not indicate whether the conjecture has been resolved.

References

Primary source

Jamie Juul, Holly Krieger, Nicole Looper, Michelle Manes, Bianca Thompson and Laura Walton, “Arboreal representations for rational maps with few critical points”, arXiv:1804.06053 (2018).

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