Electron. J. Differential Equations, Vol. 2025 (2025), No. 61, pp. 1-19.

Reading multiplicity in unfoldings from epsilon-neighborhoods of orbits

Renato Huzak, Pavao Mardesic, Maja Resman, Vesna Zupanovic

Abstract:
We consider generic analytic 1-parameter unfoldings of saddle-node germs of analytic vector fields on the real line, their time-one maps and the Lebesgue measure of \(\varepsilon\)-neighborhoods of the orbits of these time-one maps. The box dimension of an orbit gives the asymptotics of the principal term of this Lebesgue measure and it is known that it is discontinuous at bifurcation parameters. To recover continuous dependence of the asymptotics on the parameter, here we expand asymptotically the Lebesgue measure of \(\varepsilon\)-neighborhoods of orbits of time-one maps in a Chebyshev system, uniformly with respect to the bifurcation parameter. We use Ecalle-Roussarie-type compensators. We show how the number of fixed points of the time-one map born in the universal analytic unfolding of the parabolic point corresponds to the number of terms vanishing in this uniform expansion of the Lebesgue measure of \(\varepsilon\)-neighborhoods of orbits.

Submitted February 21, 2025. Published June 10, 2025.
Math Subject Classifications: 37G10, 34C23, 28A80, 37C45, 37M20.
Key Words: Unfoldings; epsilon-neighborhoods; compensators; Chebyshev scale.
DOI: 10.58997/ejde.2025.61

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Renato Huzak \newline Hasselt University
Campus Diepenbeek
Agoralaan Gebouw D
Diepenbeek 3590, Belgium
email: renato.huzak@uhasselt.be
Pavao Mardesic
Universite Bourgogne Europe
CNRS, IMB UMR 5584, 21000 Dijon, France
email: pavao.mardesic@u-bourgogne.fr
Maja Resman
University of Zagreb
Faculty of Science, Department of Mathematics
Bijenicka cesta 30 / Horvatovac 102a
10000 Zagreb, Croatia
email: maja.resman@math.hr
Vesna Zupanovic
University of Zagreb
Faculty of Electrical Engineering and Computing
Unska 3, 10000 Zagreb, Croatia
email: vesna.zupanovic@fer.unizg.hr

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