SO and Sp Chern-Simons at Large N
  We study the large N limit of SO(N) and Sp(N) Chern-Simons gauge theory on S^3 and identify its closed string dual as topological strings on an orientifold of the small resolution of the conifold. Applications to large N dualities for N=1 supersymmetric gauge systems in 4 dimensions are also discussed. 
S. Sinha and C. Vafa