Bounded cochains on 3-manifolds
Danny Calegari
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We study the large-scale geometry of 3-manifolds whose fundamental groups admit 1-cochains with certain geometric properties, as an intermediate step towards the geometrization conjecture.
An unbounded 1-cochain with bounded coboundary is {\it weakly
uniform\/} if the coarse level sets are coarsely connected, and {\it
uniform\/} if the coarse level sets are coarsely connected and
coarsely simply connected.
{\bf Theorem 1.} A 1-cochain on a 3-manifold is weakly uniform iff it
is uniform.
This theorem is a coarse analogue of Stallings fibration theorem, and
Novikov's theorem about taut foliations; it may also be thought of as
a kind of "coarse Scott core theorem".
Theorem 2: If M admits a uniform 1-cochain, then either M is homotopic to a Seifert fibered or solv manifold, or contains a reducing torus, or the fundamental group is word-hyperbolic. Moreover in the last case, there is a precise quasi-isometric model for the universal cover of M, analogous to a singular solv metric, and a dynamical system which conjecturally should produce a hyperbolic structure on M.
This theorem shows that such manifolds M are good generalizations of manifolds which fiber or slither over the circle, and have a similar associated "pseudo Anosov package".
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