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Spherical normal forms for germs of parabolic line biholomorphisms

Part of: Complex dynamical systems Differential equations in the complex domain

Published online by Cambridge University Press:  07 April 2025

LOÏC TEYSSIER
LOÏC TEYSSIER*
Affiliation:
Laboratoire IRMA (UMR 7501), Université de Strasbourg—CNRS, Strasbourg, France
*
e-mail: teyssier@math.unistra.fr
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Abstract

We address the inverse problem for holomorphic germs of a mapping of the complex line near a fixed point which is tangent to the identity. We provide a preferred parabolic map $\Delta $ realizing a given Birkhoff–Écalle–Voronin modulus $\psi $ and prove its uniqueness in the functional class we introduce. The germ is the time-$1$ map of a Gevrey formal vector field admitting meromorphic sums on a pair of infinite sectors covering the Riemann sphere. For that reason, the analytic continuation of $\Delta $ is a multivalued map admitting finitely many branch points with finite monodromy. In particular, $\Delta $ is holomorphic and injective on an open slit sphere containing $0$ (the initial fixed point) and $\infty $, where the companion parabolic point is situated under the involution ${-1}/{\mathrm {Id}}$. One finds that the Birkhoff–Écalle–Voronin modulus of the parabolic germ at $\infty $ is the inverse $\psi ^{\circ -1}$ of that at $0$.

Keywords

parabolic fixed-pointnormal formsinverse problemparabolic renormalization

MSC classification

Primary: 37F45: Holomorphic families of dynamical systems; the Mandelbrot set; bifurcations 37F75: Holomorphic foliations and vector fields
Secondary: 34M35: Singularities, monodromy, local behavior of solutions, normal forms 34M50: Inverse problems (Riemann-Hilbert, inverse differential Galois, etc.)

Information

Type
Original Article
Information
Ergodic Theory and Dynamical Systems , Volume 45 , Issue 10 , October 2025 , pp. 3255 - 3304
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Copyright
© The Author(s), 2025. Published by Cambridge University Press

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