  General principles of quantum field theory imply that there exists an
operator product expansion (OPE) for Wightman functions in Minkowski momentum
space that converges for arbitrary kinematics. This convergence is guaranteed
to hold in the sense of a distribution, meaning that it holds for correlation
functions smeared by smooth test functions. The conformal blocks for this OPE
are conceptually extremely simple: they are products of 3-point functions. We
construct the conformal blocks in 2-dimensional conformal field theory and show
that the OPE in fact converges pointwise to an ordinary function in a specific
kinematic region. Using microcausality, we also formulate a bootstrap equation
directly in terms of momentum space Wightman functions.
