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This dissertation investigates the group of quasisymmetries of the Feigenbaum Julia set, denoted as Jc. Quasisymmetry is a type of geometric mapping that preserves the qualitative structure of sets under distortion. The Feigenbaum Julia set is a non-hyperbolic quadratic Julia set, presenting a different challenge compared to hyperbolic sets. The research describes the group of topologically extendable quasisymmetric self-maps of Jc, providing the first example for an infinitely renormalizable map. The study relies on the topology and geometry of the transcendental dynamics of a related renormalization fixed point to fully determine this group.
This dissertation explores the relationship between algebraic geometry and topology, specifically how the Galois group of the algebraic closure of rational numbers (Q) affects the underlying manifold structures of complex algebraic varieties defined over Q. While algebraic isomorphisms can exist between varieties, their topological structures (like homeomorphism type) might differ. The research uses concepts like 'profinite completion' to understand these changes, as the Galois action preserves this 'profinite homotopy type'. The study investigates what algebraic-topological data is sufficient to define a manifold within a given homotopy type, how to construct these manifolds algebraically ('étale construction'), and how the Galois action can be expressed using this data.