Upper semicontinuity conjecture for the mother hedgehog

Let cΔc\in\partial\boldsymbol{\Delta} be a non-parabolic parameter, let fcf_c be the corresponding quadratic polynomial, and let HcH_c denote its mother hedgehog: if the closed Siegel disk contains a critical point, HcH_c is that closed Siegel disk; otherwise, HcH_c is the closure of the union of all hedgehogs of fcf_c. Mother hedgehog conjecture. The mother hedgehog HcH_c depends upper semicontinuously on cc. This is the indifferent-dynamical analogue of the upper semicontinuous dependence of the filled-in Julia set on the polynomial. Its resolution would provide continuity control for mother hedgehogs across non-parabolic parameters.

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Primary source

Dzmitry Dudko, Mikhail Lyubich and Nikita Selinger, “Pacman renormalization and self-similarity of the Mandelbrot set near Siegel parameters”, arXiv:1703.01206 (2019).

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