We introduce and study some deformations of complete finite-volume hyperbolic
four-manifolds that may be interpreted as four-dimensional analogues of Thurston’s
hyperbolic Dehn filling.
We construct in particular an analytic path of complete, finite-volume cone four-manifolds
that interpolates between two hyperbolic four-manifolds
and
with the
same volume
.
The deformation looks like the familiar hyperbolic Dehn filling paths that occur in
dimension three, where the cone angle of a core simple closed geodesic varies monotonically
from
to
. Here, the
singularity of
is an immersed geodesic surface whose cone angles also vary monotonically from
to . When a cone
angle tends to
a small core surface (a torus or Klein bottle) is drilled, producing a new
cusp.
We show that various instances of hyperbolic Dehn fillings may arise,
including one case where a degeneration occurs when the cone angles tend to
, like
in the famous figure-eight knot complement example.
The construction makes an essential use of a family of four-dimensional deforming
hyperbolic polytopes recently discovered by Kerckhoff and Storm.