Brane webs and O5-planes

We explore the properties of five-dimensional supersymmetric gauge theories living on 5-brane webs in orientifold 5-plane backgrounds. This allows constructing quiver gauge theories with alternating USp(2N) and SO(N) gauge groups with fundamental matter, and thus leads to the existence of new 5d fixed point theories. The web description can be further used to study non-perturbative phenomena such as enhancement of symmetry and duality. We further suggest that one can use these systems to engineer 5d SO group with spinor matter. We present evidence for this claim.