Across the Boundary Conjecture for Mandelbrot copies

Let a Mandelbrot copy in Sp{\mathcal S}_p cut across the boundary between two escape regions at a parabolic point p{\mathfrak p} of period qq. The associated dynamic configuration includes periodic rays θq\theta_q, co-periodic rays θ\theta, and their twin rays θ^\widehat{\theta}; the marked critical point is aa and the free critical point is a-a. Across the Boundary Conjecture. There are four parameter rays landing on p{\mathfrak p}, and four corresponding triads in the Julia set for p{\mathfrak p}. If pqp\ne q, the periodic dynamic rays θq\theta_q land at the point of period at least two between aa and a-a; the co-periodic rays θ\theta land at the root point of the hyperbolic component containing 2a2a; and the twin rays θ^\widehat{\theta} land on a preimage of a-a. The midpoint between the periodic landing point and the landing point of the twin rays is always the free critical point a-a. If p{\mathfrak p} is self-dual, as for a Type A component, the twin rays land precisely at the root point of 2a-2a. This conjecture seeks a general description of the ray configuration when a Mandelbrot copy crosses an escape-region boundary; the source gives illustrative examples but no resolution.

Sources & referencesView supporting material

Primary source

Araceli Bonifant and John Milnor, “Cubic Polynomial Maps with Periodic Critical Orbit, Part III: Tessellations and Orbit Portraits”, arXiv:2503.08868 (2025).

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