Cones, Tri-Sasakian Structures and Superconformal Invariance
  In this note we show that rigid N=2 superconformal hypermultiplets must have target manifolds which are cones over tri-Sasakian metrics. We comment on the relation of this work to cone-branes and the AdS/CFT correspondence. 
G.W.Gibbons and P.Rychenkova