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On the geometry of a proposed curve complex analogue for
The group \Out of outer automorphisms of the free group has been an object
of active study for many years, yet its geometry is not well understood.
Recently, effort has been focused on finding a hyperbolic complex on which
\Out acts, in analogy with the curve complex for the mapping class group.
Here, we focus on one of these proposed analogues: the edge splitting complex
\ESC, equivalently known as the separating sphere complex. We characterize
geodesic paths in its 1-skeleton algebraically, and use our characterization to
find lower bounds on distances between points in this graph.
Our distance calculations allow us to find quasiflats of arbitrary dimension
in \ESC. This shows that \ESC: is not hyperbolic, has infinite asymptotic
dimension, and is such that every asymptotic cone is infinite dimensional.
These quasiflats contain an unbounded orbit of a reducible element of \Out.
As a consequence, there is no coarsely \Out-equivariant quasiisometry between
\ESC and other proposed curve complex analogues, including the regular free
splitting complex \FSC, the (nontrivial intersection) free factorization
complex \FFZC, and the free factor complex \FFC, leaving hope that some of
these complexes are hyperbolic.Comment: 23 pages, 6 figure
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