The PL-methods for hyperbolic 3-manifolds to prove tameness

Abstract

Using PL-methods, we prove the Marden's conjecture that a hyperbolic 3-manifold $M$ with finitely generated fundamental group and with no parabolics are topologically tame. Our approach is to form an exhaustion $M_i$ of $M$ and modify the boundary to make them 2-convex. We use the induced path-metric, which makes the submanifold $M_i$ negatively curved and with Margulis constant independent of $i$. By taking the convex hull in the cover of $M_i$ corresponding to the core, we show that there exists an exiting sequence of surfaces $\Sigma_i$. Some of the ideas follow those of Agol. We drill out the covers of $M_i$ by a core $\core$ again to make it negatively curved. Then the boundary of the convex hull of $\Sigma_i$ is shown to meet the core. By the compactness argument of Souto, we show that infinitely many of $\Sigma_i$ are homotopic in $M - \core^o$. Our method should generalize to a more wider class of piecewise hyperbolic manifolds.