Four-point correlators of BPS operators in N=4 SYM at order g4

We study the large N degeneracy in the structure of the four-point amplitudes of ½ BPS operators of arbitrary weight k in perturbative N = 4 SYM theory. At one loop (order g2) this degeneracy manifests itself in a smaller number of independent conformal invariant functions describing the amplitude, compared to AdS5 supergravity results. To study this phenomenon at the two-loop level (order g4) we consider a particular N = 2 hypermultiplet projection of the general N = 4 amplitude. Using the formalism of N = 2 harmonic superspace we then explicitly compute this four-point correlator at two loops and identify the corresponding conformal invariant functions. In the cases of ½ BPS operators of weight k = 3 and k = 4 the one-loop large N degeneracy is lifted by the two-loop corrections. However, for weight k > 4 the degeneracy is still there at the two-loop level. This behavior suggests that for a given weight k the degeneracy will be removed if perturbative corrections of sufficiently high order are taken into account. These results are in accord with the AdS/CFT duality conjecture