Ghost story. II. The midpoint ghost vertex. (arXiv:0908.0055v2 [hep-th] UPDATED)

We construct the ghost number 9 three strings vertex for OSFT in the naturalnormal ordering. We find two versions, one with a ghost insertion at z=i and atwist-conjugate one with insertion at z=-i. For this reason we call themmidpoint vertices. » Full text »