Incompressibility and normal minimal surfaces

Abstract

In this paper we describe a procedure for refining the given triangulation of a 3-manifold that scales the PL-metric according to a given weight function while creating no new normal surfaces. It is known that an incompressible surface $F$ in a triangulated 3-manifold $M$ is isotopic to a normal surface that is of minimal PL-area in the isotopy class of $F$. Using the above scaling refinement we prove the converse. If $F$ is a surface in a closed 3-manifold $M$ such that for any triangulation $\tau$ of $M$, $F$ is isotopic to a $\tau$-normal surface $F(\tau )$ that is of minimal PL-area in its isotopy class, then we show that $F$ is incompressible.

10 pages, 2 figures