Abstract
A-manifolds and B-manifolds, introduced by Gray (1978), are two significant classes of Einstein-like Riemannian manifolds. A Riemannian manifold is Ricci parallel if and only if it is simultaneously an A-manifold and a B-manifold. The present paper proves that both focal submanifolds of each isoparametric hypersurface in unit spheres with g = 4 distinct principal curvatures are A-manifolds. As for the focal submanifolds with g = 6, m = 1 or 2, only one is an A-manifold, and neither is a B-manifold.
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Li, Q., Yan, W. On Ricci tensor of focal submanifolds of isoparametric hypersurfaces. Sci. China Math. 58, 1723–1736 (2015). https://doi.org/10.1007/s11425-014-4928-6
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DOI: https://doi.org/10.1007/s11425-014-4928-6