2-LOOP SCALAR DIAGRAMS FROM STRING THEORY

We show how to obtain correctly normalized expressions for the Feynman diagrams of Phi(3) theory with an internal U(N) symmetry group, start ing from tachyon amplitudes of the open bosonic string, and suitably p erforming the zero-slope limit by giving an arbitrary mass m to the ta chyon. In particular we present explicit results for the two-loop ampl itudes of Phi(3) theory, in preparation for the more interesting case of multiloop amplitudes of non-abelian gauge theories.