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Trivial holonomy gives a product foliated neighbourhood
Statement
Assume (The countable-choice principle used in the foliation pair). Let be a regular foliation and a compact leaf whose holonomy representation is trivial (equivalently, whose holonomy group is the trivial group) (The holonomy representation and the holonomy group of a leaf). Then the finite-holonomy normal model with is with , and has arbitrarily small saturated neighbourhoods foliated-diffeomorphic to products with the product foliation by the slices . In particular every leaf of is compact and diffeomorphic to , and has a fundamental system of product foliated neighbourhoods.
Facts & Assumptions
Given: A regular foliation and a compact leaf whose holonomy representation is trivial.
The holonomy cover is the connected covering with ; when is trivial, , so has degree one and (The holonomy cover of a leaf, The holonomy representation and the holonomy group of a leaf).
The finite-holonomy normal model of is with the diagonal action; for it is the product with the product foliation by the slices, and the product carries its canonical product smooth structure (The finite-holonomy normal model of a compact leaf, Products of smooth manifolds have a canonical product smooth structure).
A compact leaf with finite holonomy is stable: every neighbourhood contains a saturated neighbourhood foliated-diffeomorphically onto a neighbourhood of the central leaf of the normal model (Local Reeb stability for compact leaves with finite holonomy, Saturated neighbourhoods of a leaf).
A diffeomorphism of a neighbourhood of the central leaf onto a product restricts to the slices, which are diffeomorphic to (Diffeomorphisms and local diffeomorphisms of manifolds).
Proof
(The holonomy cover is trivial.) With trivial, the kernel is all of , so the covering associated with the kernel has ; a covering of degree one is a diffeomorphism, and we identify [F1].
(The model and the neighbourhood.) With the finite-holonomy normal model is the product with the product foliation by slices [F2]. The local Reeb stability theorem applies because the holonomy group is finite (indeed trivial), and gives, for every neighbourhood of , a saturated neighbourhood foliated-diffeomorphically onto a neighbourhood of the central leaf, which after shrinking is a product with the product foliation [F2, F3].
(Fundamental system and leaves.) The product neighbourhoods for shrinking transverse disks form a fundamental system of neighbourhoods of the central leaf, and each leaf of the product foliation is a slice , compact and diffeomorphic to [F2, F4]. Hence has a fundamental system of product foliated neighbourhoods whose leaves are compact and diffeomorphic to .
Depends on
- Local Reeb stability for compact leaves with finite holonomy
- The finite-holonomy normal model of a compact leaf
- The holonomy representation and the holonomy group of a leaf
- Saturated neighbourhoods of a leaf
- Products of smooth manifolds have a canonical product smooth structure
- Diffeomorphisms and local diffeomorphisms of manifolds
- The countable-choice principle used in the foliation pair
- The holonomy cover of a leaf
Used by
- Finiteness of the fundamental group is sufficient, but not necessary, for Reeb stability Corollary
- A compact leaf with infinite fundamental group can still have trivial holonomy Counterexample
- The product foliation near a compact leaf with trivial holonomy Example
- A compact holonomy-free codimension-one foliation is fibered over its leaf space Lemma
- Closedness of compact leaves diffeomorphic to a finite-fundamental-group leaf Lemma
- Compact leaves with finite holonomy form an open saturated set Lemma
- In a transversely oriented codimension-one foliation a compact leaf with finite fundamental group has trivial holonomy Lemma
Dependency tree · two levels
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Sources
- Ieke Moerdijk and Janez Mrčun, Introduction to Foliations and Lie Groupoids (Cambridge Studies in Advanced Mathematics 91, 2003) (standard reference, not scraped)
- Danny Calegari, Foliations and the Geometry of 3-Manifolds (Oxford Mathematical Monographs; complete author-hosted PDF) (standard reference, not scraped)