Hyper-Kahler Sigma Models on (Co)tangent Bundles with SO(n) isometry
  We construct N=2 supersymmetric nonlinear sigma models whose target spaces are tangent as well as cotangent bundles over the quadric surface Q^{n-2} = SO(n)/[SO(n-2)\times U(1)]. We use the projective superspace framework, which is an off-shell formalism of N=2 supersymmetry. 
Masato Arai, Muneto Nitta