Jones's index conjecture for quadratic rational maps
Let be a global field, let have degree two, and let be the infinite rooted binary tree of preimages of a root under . Write for the image of the associated arboreal Galois representation. Jones's conjecture. One has
if and only if at least one of the following holds: is postcritically finite; the two critical points and satisfy for some ; the root is periodic under ; or a nontrivial Möbius transformation commuting with fixes . 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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