String-generated quartic scalar interactions
  The {\em cutting and sewing} procedure is used for getting two-loop order Feynman diagrams of $\Phi^{4}$-theory with an internal SU(N) symmetry group, starting from tachyon amplitudes of the open bosonic string theory. In a suitably defined field theory limit, we reproduce the field theory amplitudes properly normalized and expressed in the Schwinger parametrization. 
R. Marotta, F. Pezzella