Factorization of the Two Loop Four-Particle Amplitude in Superstring   Theory Revisited
  We study in detail the factorization of the newly obtained two-loop four-particle amplitude in superstring theory. In particular some missing factors from the scalar correlators are obtained correctly, in comparing with a previous study of the factorization in two-loop superstring theory. Some details for the calculation of the factorization of the kinematic factor are also presented. 
Zhi-Guang Xiao, Chuan-Jie Zhu