A New World Sheet Field Theory
  A second quantized field theory on the world sheet is developed for summing planar graphs of the phi^3 theory. This is in contrast to the earlier work, which was based on first quantization. The ground state of the model is investigated with the help of a variational ansatz. In complete agreement with standard perturbation theory, the infinities encountered in carrying out this calculation can be eliminated by the renormalization of the parameters of the model. We also find that, as in the earlier work, in the ground state, graphs form a dense network (condensate) on the world sheet. 
Korkut Bardakci