Consistency Conditions for Fivebrane in M Theory on R^5/Z_2 Orbifold
  We derive some consistency conditions for fivebrane in M theory on R^5/Z_2 orbifold from the quantization law for the antisymmetric tensor field. We construct consistent fivebrane configurations in R^5/Z_2 type orbifold that exhibit the correct low energy dynamics of N=2 SQCD in four dimensions with symplectic and orthogonal gauge groups. This leads us to propose the M theory realization of orientifold four-planes of various types, and we study their properties by applying the consistency conditions. 
Kentaro Hori (UC Berkeley/LBNL)