In mathematics, Novikov's compact leaf theorem, named after Sergei Novikov, states that
- A codimension-one foliation of a compact 3-manifold whose universal covering space is not contractible must have a compact leaf.
Novikov's compact leaf theorem for S
Theorem: A smooth codimension-one foliation of the 3-sphere S has a compact leaf. The leaf is a torus T bounding a solid torus with the Reeb foliation.
The theorem was proved by Sergei Novikov in 1964. Earlier, Charles Ehresmann had conjectured that every smooth codimension-one foliation on S had a compact leaf, which was known to be true for all known examples; in particular, the Reeb foliation has a compact leaf that is T.
Novikov's compact leaf theorem for any M
In 1965, Novikov proved the compact leaf theorem for any M:
Theorem: Let M be a closed 3-manifold with a smooth codimension-one foliation F. Suppose any of the following conditions is satisfied:
- the fundamental group is finite,
- the second homotopy group ,
- there exists a leaf such that the map induced by inclusion has a non-trivial kernel.
Then F has a compact leaf of genus g ≤ 1.
In terms of covering spaces:
A codimension-one foliation of a compact 3-manifold whose universal covering space is not contractible must have a compact leaf.
References
- S. Novikov. The topology of foliations//Trudy Moskov. Mat. Obshch, 1965, v. 14, p. 248–278.
- I. Tamura. Topology of foliations — AMS, v.97, 2006.
- D. Sullivan, Cycles for the dynamical study of foliated manifolds and complex manifolds, Invent. Math., 36 (1976), p. 225–255.