dS/CFT and the operator product expansion
  Global conformal invariance determines the form of two and three-point functions of quasi-primary operators in a conformal field theory, and generates nontrivial relations between terms in the operator product expansion. These ideas are generalized to the principal and complementary series representations, which play an important role in the conjectured dS/CFT correspondence. The conformal partial wave expansions are constructed for these representations which in turn determine the operator product expansion. This leads us to conclude that conformal field theories containing such representations have essential singularities, so cannot be realized as conventional field theories. 
Atreya Chatterjee and David A. Lowe
hep-th