  We study the asymptotic geometry of the spin foam partition function for a
large class of models, including the models of Barrett and Crane, Engle,
Pereira, Rovelli and Livine, and, Freidel and Krasnov.
  The asymptotics is taken with respect to the boundary spins only, no
assumption of large spins is made in the interior. We give a sufficient
criterion for the existence of the partition function. We find that geometric
boundary data is suppressed unless its interior continuation satisfies certain
accidental curvature constraints. This means in particular that most Regge
manifolds are suppressed in the asymptotic regime. We discuss this explicitly
for the case of the configurations arising in the 3-3 Pachner move. We identify
the origin of these accidental curvature constraints as an incorrect twisting
of the face amplitude upon introduction of the Immirzi parameter and propose a
way to resolve this problem, albeit at the price of losing the connection to
the SU(2) boundary Hilbert space.
  The key methodological innovation that enables these results is the
introduction of the notion of wave front sets, and the adaptation of tools for
their study from micro local analysis to the case of spin foam partition
functions.
