Abstract
All nonhyperbolic automorphisms of the 2-torus are not structurally stable, and it is generally impossible to predict the dynamics of their arbitrarily small perturbations. In this paper, given a representative of each algebraic conjugacy class of nonperiodic nonhyperbolic maps, a one-parameter family of diffeomorphisms is constructed, in which the zero value of the parameter corresponds to the given map and the nonzero values, to Morse–Smale diffeomorphisms. According to results of V. Z. Grines and A. N. Bezdenezhnykh, a Morse–Smale diffeomorphism of a closed orientable surface which induces a nonperiodic action on the fundamental group has nonempty heteroclinic set. It is proved that, in all of the constructed families, the diffeomorphisms corresponding to nonzero parameter values have nonempty orientable heteroclinic sets in which the number of orbits is determined by the automorphism being perturbed.
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Notes
At the points \(z\in(k-1/2,k+1/2)\), \(k\in\mathbb Z\), the differentiability of this function follows from that of the functions \(\tan(\pi z)\) and \(\arctan(z)\); at the points \(k+1/2\), \(k\in\mathbb Z\), it follows from the coincidence of the left and right derivatives of the function at these points.
Geometrically, this means that the graph of \(\phi_{\mathrm u}(x-(q+1))\) lies below that of \(\phi_{\mathrm u}(x-q)\), so that the point of intersection is below this graph as well (and it is on the right of it, because \(\phi_{\mathrm s}\) is monotone).
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Funding
The publication was prepared within the framework of the Academic Fund Program at the HSE University in 2021–2022 (grant no. 21-04-004), except for the work on Sec. 2, which was supported by the Laboratory of Dynamical Systems and Applications NRU HSE, grant of the Ministry of Science and Higher Education of the Russian Federation (agreement no. 075-15-2022-1101).
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Translated from Matematicheskie Zametki, 2023, Vol. 114, pp. 229–243 https://doi.org/10.4213/mzm13612.
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Grines, V.Z., Mints, D.I. & Chilina, E.E. Perturbations of Nonhyperbolic Algebraic Automorphisms of the 2-Torus. Math Notes 114, 187–198 (2023). https://doi.org/10.1134/S0001434623070209
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DOI: https://doi.org/10.1134/S0001434623070209