The zero-slope limit of Witten's string field theory with Chan-Paton factors

I demonstrate that open-string field theory with Chan-Paton factors has Yang-Mills theory as its off-shell zero-slope limit. I first add Chan-Paton group factors both to Witten's string field theory and to a non-oriented extension of it. The quadratic and cubic interactions between massless fields are calculated in the zero-slope limit by means of the Neumann functions computed for Witten's theory by Gross and Jevicki and by Cremmer, Schwimmer and Thorn. I show that the only other terms (up to renormalisation) appearing in the zero-slope limit are those from tree-level interactions between four massless fields. These are evaluated off-shell using the conformal mapping and Neumann function techniques developed by Giddings, by Sloan, and by Samuel. The resulting lagrangian is Yang-Mills theory in the Feynman-Lorentz-Baulieu-Thierry-Mieg gauge. (orig.)