Four-Impurity Operators and String Field Theory Vertex in the BMN   Correspondence
  In the context of the Penrose/BMN limit of the AdS/CFT correspondence, we consider four-impurity BMN operators in Yang-Mills theory, and demonstrate explicitly their correspondence to four-oscillator states in string theory. Using the dilatation operator on the gauge-theory side of the correspondence, we calculate matrix elements between four-impurity states. Since conformal dimensions of gauge-theory operators correspond to light-cone energies of string states, these matrix elements may be compared with the string-theory light-cone Hamiltonian matrix elements calculated in the plane-wave background using the string field theory vertex. We find that the two calculations agree, extending the cases of two- and three-impurity operators considered in the literature using BMN gauge-theory quantum mechanics. The results are also in agreement with calculations in the literature based on perturbative gauge-theory methods. 
P. Matlock, K. S. Viswanathan