World-Sheets from N=4 Super Yang-Mills
  We examine whether the free energy of N=4 super Yang-Mills theory (SYM) in four dimensions corresponds to the partition function of the AdS_5 x S^5 superstring when corresponding operators are inserted into both theories. We obtain a formal free energy of N=4 U(N) SYM in four dimensions generated by the Feynman graph expansion to all orders of the 't Hooft coupling expansion with arbitrary N. This free energy is written as the sum over discretized closed two-dimensional surfaces that are identified with the world-sheets of the string. We compare this free energy with a formal partition function of the discretized AdS_5 x S^5 superstring with the kappa-symmetry fixed in the killing gauge and in the expansion corresponding to the weak 't Hooft coupling expansion in the SYM. We find common properties on both sides, although further studies are required to obtain a more precise comparison. Our result suggests a mechanism for how the world-sheet appears dynamically from N=4 SYM, thus enabling us to derive how the AdS_5 x S^5 superstring is reproduced in the AdS/CFT correspondence. 
Matsuo Sato