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Homomorphisms between diffeomorphism groups
Published online by Cambridge University Press: 04 July 2013
Abstract
For $r\geq 3$,
$p\geq 2$, we classify all actions of the groups
${ \mathrm{Diff} }_{c}^{r} ( \mathbb{R} )$ and
${ \mathrm{Diff} }_{+ }^{r} ({S}^{1} )$ by
${C}^{p} $-diffeomorphisms on the line and on the circle. This is the same as describing all non-trivial group homomorphisms between groups of compactly supported diffeomorphisms on 1-manifolds. We show that all such actions have an elementary form, which we call topologically diagonal. As an application, we answer a question of Ghys in the 1-manifold case: if
$M$ is any closed manifold, and
${\mathrm{Diff} }^{\infty } \hspace{-2.0pt} \mathop{(M)}\nolimits_{0} $ injects into the diffeomorphism group of a 1-manifold, must
$M$ be one-dimensional? We show that the answer is yes, even under more general conditions. Several lemmas on subgroups of diffeomorphism groups are of independent interest, including results on commuting subgroups and flows.
- Type
- Research Article
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- Copyright
- © Cambridge University Press, 2013
References
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