Curvature properties of pseudo-sphere bundles over paraquaternionic   manifolds
  In this paper we obtain several curvature properties of the twistor and reflector spaces of a paraquaternionic K\"{a}hler manifold and prove the existence of both positive and negative mixed 3-Sasakian structures in a principal SO(2,1)-bundle over a paraquaternionic K\"{a}hler manifold. 
Gabriel Eduard Vilcu, Rodica Cristina Voicu
math.DG