22,255 research outputs found
Slice theorem and orbit type stratification in infinite dimensions
We establish a general slice theorem for the action of a locally convex Lie
group on a locally convex manifold, which generalizes the classical slice
theorem of Palais to infinite dimensions.
We discuss two important settings under which the assumptions of this theorem
are fulfilled. First, using Gl\"ockner's inverse function theorem, we show that
the linear action of a compact Lie group on a Fr\'echet space admits a slice.
Second, using the Nash--Moser theorem, we establish a slice theorem for the
tame action of a tame Fr\'echet Lie group on a tame Fr\'echet manifold. For
this purpose, we develop the concept of a graded Riemannian metric, which
allows the construction of a path-length metric compatible with the manifold
topology and of a local addition.
Finally, generalizing a classical result in finite dimensions, we prove that
the existence of a slice implies that the decomposition of the manifold into
orbit types of the group action is a stratification
Relative Property (T) Actions and Trivial Outer Automorphism Groups
We show that every non-amenable free product of groups admits free ergodic
probability measure preserving actions which have relative property (T) in the
sense of S.-Popa \cite[Def. 4.1]{Pop06}. There are uncountably many such
actions up to orbit equivalence and von Neumann equivalence, and they may be
chosen to be conjugate to any prescribed action when restricted to the free
factors. We exhibit also, for every non-amenable free product of groups, free
ergodic probability measure preserving actions whose associated equivalence
relation has trivial outer automorphisms group. This gives in particular the
first examples of such actions for the free group on generators.Comment: Improvement in the presentation of the replacement trick.
Introduction of compressions for non-ergodic equivalence relation
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