|
J Hempel showed that the set of distances of
the Heegaard splittings (S,V,hn(V)) is
unbounded, as long as the stable and unstable laminations of h avoid
the closure of V ⊂ PML(S). Here h is a
pseudo-Anosov homeomorphism of a surface S while V is
the set of isotopy classes of simple closed curves in S bounding
essential disks in a fixed handlebody.
With the same hypothesis we show the distance of the splitting
(S,V,hn(V)) grows linearly with n, answering a
question of A Casson. In addition we prove the converse of Hempel's
theorem. Our method is to study the action of h on the curve complex
associated to S. We rely heavily on the result, due to H Masur and
Y Minsky, that the curve complex is Gromov hyperbolic.
|