Four-point functions in N=2 superconformal field theories
  Four-point correlation functions of hypermultiplet bilinear composites are analysed in N=2 superconformal field theory using the superconformal Ward identities and the analyticity properties of the composite operator superfields. It is shown that the complete amplitude is determined by a single arbitrary function of the two conformal cross-ratios of the space-time variables. 
B. U. Eden, P. S. Howe, A. Pickering, E. Sokatchev and P. C. West