Density of the rational obstructed boundary in the obstructed boundary

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Let H\mathcal{H} be a hyperbolic component of disjoint type. Define its obstructed boundary by

∂∞H={ρ∈∂D2d−2: there exists [fn]∈H with [fn]→∞ in M⁡d,fm and ρ([fn])→ρ}.\partial^\infty\mathcal{H}=\{\rho\in\partial\mathbb{D}^{2d-2}:\text{ there exists }[f_n]\in\mathcal{H}\text{ with }[f_n]\to\infty\text{ in }\operatorname{\mathcal{M}}_{d,\text{fm}}\text{ and }\boldsymbol{\rho}([f_n])\to\rho\}.

Let ∂Q∞H\partial^\infty_{\mathbb{Q}}\mathcal{H} be the subset of ∂∞H\partial^\infty\mathcal{H} for which all indifferent multipliers are rational, of the form e2πip/qe^{2\pi i p/q}. The rational-boundary density conjecture.

∂∞H=∂Q∞H‾.\partial^\infty\mathcal{H}=\overline{\partial^\infty_{\mathbb{Q}}\mathcal{H}}.

Consequently, the natural extension of the multiplier map identifies the regular boundary as

∂reg⁡H≅∂D2d−2−∂Q∞H‾−ρ(∂exc⁡H).\partial_{\operatorname{reg}}\mathcal{H}\cong\partial\mathbb{D}^{2d-2}-\overline{\partial^\infty_{\mathbb{Q}}\mathcal{H}}-\boldsymbol{\rho}(\partial_{\operatorname{exc}}\mathcal{H}).

This would describe the boundary at infinity through obstructed geometrically finite maps and support an extension of the quadratic-like theory using sector renormalization, but the statement is presented as a conjecture.

References

Primary source

Dzimitry Dudko and Yusheng Luo, “Sierpinski carpet hyperbolic components of disjoint type are bounded”, arXiv:2509.25658 (2025).

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