H. Itoyama et A. Tsuchiya, USp(2k) matrix model - Schwinger-Dyson equations and closed-open string interactions, PROG T PHYS, 101(6), 1999, pp. 1371-1390
We derive the Schwinger-Dyson/loop equations for the USp(2k) matrix model w
hich close among the closed and open Wilson loop variables. These loop equa
tions exhibit a complete set of the joining and splitting interactions requ
ired for nonorientable Type I superstrings. The open loops realize the SO(2
n(f)) Chan-Paton factor and their linearized loop equations give the mixed
Dirichlet/Neumann boundary conditions.