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On close to linear cocycles. (English) Zbl 0879.54048

Summary: If we have a flow \((X,\mathbb{Z}^m)\) and a cocyle \(h\) on this flow, \(h:X \times \mathbb{Z}^m \to \mathbb{R}^m\), then \(h\) is called close to linear if \(h\) can be written as the direct sum of a linear (constant) cocycle and a cocycle in the closure of the coboundaries. Many of the desirable consequences of linearity hold for such cocycles and, in fact, a close to linear cocycle is cohomologous to a cocycle which is norm close to a linear one. Furthermore in the uniquely ergodic case all cocycles are close to linear. We also establish that a close to linear cocycle which is covering is cohomologous to one with the special property that it can be extended by piecewise linearity to an invertible cocycle from \(X\times \mathbb{R}^m\) to itself. This implies that a suspension obtained from a close to linear cocycle is isomorphic to a time change of the suspension obtained from the identity cocycle.

MSC:

54H20 Topological dynamics (MSC2010)
37C10 Dynamics induced by flows and semiflows
28D10 One-parameter continuous families of measure-preserving transformations
37A99 Ergodic theory
28D15 General groups of measure-preserving transformations
Full Text: DOI

References:

[1] Hillel Furstenberg, Harvey B. Keynes, Nelson G. Markley, and Michael Sears, Topological properties of \?\(^{n}\) suspensions and growth properties of \?\(^{n}\) cocycles, Proc. London Math. Soc. (3) 66 (1993), no. 2, 431 – 448. · Zbl 0790.58032 · doi:10.1112/plms/s3-66.2.431
[2] H. B. Keynes, and M. Sears, Time changes for \(\mathbb {R}^n\) flows and suspensions, Pacific J Math., 130 No 1 (1987), 97-113. · Zbl 0594.58039
[3] H. B. Keynes, N. G. Markley, and M. Sears, On the structure of minimal \?\(^{n}\) actions, Quaestiones Math. 16 (1993), no. 1, 81 – 102. · Zbl 0808.54029
[4] H. B. Keynes, N. G. Markley, and M. Sears, Ergodic averages and integrals of cocycles, Acta Math. Univ. Comemanae LXIV (1995), 123–139. · Zbl 0932.37001
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