Some problems in hyperbolic 3-manifolds
Yair Minsky
June 9, 2004
Geometry from topology
The geometrization conjecture supplies necessary and sufficient
topological conditions for a 3-manifold M to admit a hyperbolic
structure. When M is closed this structure is unique by Mostow
rigidity. There is currently only incomplete understanding of how to
predict, from topological data, the geometric properties of the
hyperbolic metric. For example, how may we predict the volume, the
injectivity radius, the number of closed geodesics with a given length
bound, etc. etc.?
(Culler-Shalen et al have given some lower volume bounds from topological data,
e.g. first betti numbers. Weeks' "Snappea" program gives
precise numerical estimates from triangulation data).
-
A "gluing problem": Let M1,M2 be compact 3-manifolds and
f:¶M1 ® ¶M2 be a homeomorphism.
Give a uniform bilipschitz model for M = M1 Èf M2, with
estimates depending only on the topology of Mi and the map f.
-
Incompressible case: If ¶Mi are incompressible, then
the gluing problem reduces to (a) the model manifold constructed
by Brock-Canary-Minsky for the solution of the Ending Lamination
Conjecture, and (b) Thurston's "bounded image theorem" which
says when ¶Mi is acylindrical that
the image of the "skinning map" in Teich(¶Mi) is
compact. Given a topological description of Mi, can one give a
quantitative bound on the diameter of the
skinning map image?
Structure of deformation spaces
If M is a compact hyperbolizable 3-manifold with boundary we may
consider the
space of marked hyperbolic structures on int(M), which lies
in the representation space p1(M) ® PSL(2,\mathbb C) modulo
conjugation. (More generally we may look at all discrete faithful
representations in this space, which gives manifolds
homotopy-equivalent to M).
- Give a complete topological description of this space.
(This is perhaps impossible. Although the space is enumerated by
end-invariants, its topological structure is quite complicated.
The end-invariants vary discontinuously, and Bromberg has shown the
deformation space is not locally connected).
- Bers slice: If M=S×[-1,1] then quasifuchsian
structures are parametrized by Teich(S)×Teich(S). A Bers slice
BX is the set parametrized by {X}×Teich(S). It is
homeomorphic to \mathbb R6g(S)-6.
Is the closure of BX a ball?
- What is the Hausdorff dimension of the boundary of the
deformation space?
-
Let MCG(M) denote the group of homeomorphisms of M modulo
homotopy. Describe the dynamics of MCG(M) on the representation
space. Do the convex-cocompact representations
comprise the largest open set on which the action is properly
discontinuous?
Representations of surface groups
Consider representations r:p1(S) ® PSL(2,\mathbb C) where S is a
compact surface and r is required to be parabolic on the boundary
of S.
- Cannon-Thurston maps: If r
is discrete and faithful, show that there is a continuous
equivariant map from S1 to S2 (where p1(S) acts on S1
via any Fuchsian representation and PSL(2,\mathbb C) acts on S2 by
Möbius transformations). This is known when r has
"bounded geometry" (lower bound on injectivity radius),
and there have been a number of extensions, notably a
complete solution by McMullen when S is a one-holed torus. There
is a general form of this conjecture for any finitely-generated
group replacing S1 by the Gromov boundary.
A positive solution would complete our picture of the
action of a Kleinian group on the 2-sphere.
- Bowditch's conjecture: Consider the quantity
where g varies over simple (non-self-intersecting) closed
curves in S, lr
denotes translation distance of the image in \mathbb H3, and
l0 denotes translation length in some Fuchsian structure on
S. Show that rr > 0 if and only if r is quasi-fuchsian.
This is known if r is discrete and faithful, but not for general
representations. I.e. show that if r is indiscrete or nonfaithful
then rr=0.
This would be trivial if g were not required to be simple.
-
Simple loop conjecture for representations: philosophically related to
Bowditch's
conjecture. If the kernel of r is nonempty, does it contain
a simple element?
- An interesting special case of (*):
Consider the action of MCG(one-holed torus)=PSL(2,\mathbb Z) on
the representation space for the one-holed torus. This space
may be parametrized (through traces of generators) as \mathbb C3,
and the group action is generated by (x,y,z) ® (x,y,xy-z)
and (x,y,z) ® (y,z,x).
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On 14 Jan 2005, 13:09.