Ricci curvature of double manifolds via isoparametric foliations

For a compact minimal isoparametric hypersurface Yn in Sn+1(1), which separates Sn+1(1) into S+n+1 and S−n+1, one can get double manifolds D(S+n+1) and D(S−n+1). Inspired by Tang, Xie and Yan's work on scalar curvature of such manifolds with isoparametric foliations (cf. [25]), we study Ricci curvature of them with isoparametric foliations in the last part.