# Example of dynamical system $M$ such that $M \rightarrow \mathbf{R}\backslash M$ is not locally trivial?

Let $\Phi: M \times \mathbf{R} \rightarrow M$ be a smooth dynamical system having no periodic orbits, i.e. such that the canonical map $\pi:M \rightarrow \mathbf{R}\backslash M$ is a principal $\mathbf{R}$-bundle. Is $\pi$ always locally trivial? If not, are there any nice (not too contrived/complicated) counterexamples? Which conditions ensure $\pi$ to be locally trivial?

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The answer is negative. Take, for instance, the irrational foliation of the flat 2-torus by geodesics with the obvious ${\mathbb R}$ action via translations along leaves.
A necessary and sufficient condition for the ${\mathbb R}$ action to come from a fibration is that the action is proper, this follows, for instance, from the slice theorem.
Nice answer, I was hoping for something along these lines. Could you explain why properness is necessary for existence of slices? I mean we only have a local condition on the action (which implies properness, locally), but a locally proper group action need not be proper. Regarding the terminology: Many people take principal $G$-bundles to be locally trivial, but many don't (e.g. Husemöller). –  Nicolas Schmidt May 15 '12 at 17:30