Chi, Quo-Shin Isoparametric hypersurfaces with four principal curvatures. II. (English) Zbl 1243.53094 Nagoya Math. J. 204, 1-18 (2011). The author shows that an isoparametric hypersurface with four principal curvatures and multiplicities \((3,4)\) in \(S^{15}\) is one constructed by Ozeki and Takeuchi and Ferus, Karcher, and Munzner, referred to collectively as of OT-FKM type. This new approach also gives a considerably simpler proof, that an isoparametric hypersurface with four principal curvatures in spheres with the multiplicity constraint \(m_{2}\geq 2m_{1}-1\) is of OT-FKM type, which left unsettled exactly the four anomalous multiplicity pairs \((4,5), (3,4), (7,8)\) and \((6,9)\), where the last three are closely tied, respectively, with the quaternion algebra, the octonion algebra, and the complexified octonion algebra, whereas the first stands alone in that it cannot be of OT-FKM type. The cases for the multiplicity pairs \((4,5), (6,9)\), and \((7,8)\) remain open now. For part I, cf. [Th. E. Cecil, Sh.-Q. Chi, G. R. Jensen, Ann. Math. (2) 166, No. 1, 1–76 (2007; Zbl 1143.53058)]; see also [the author, Nagoya Math. J. 193, 129–154 (2009; Zbl 1165.53032)]. Reviewer: Jan Kurek (Lublin) Cited in 2 ReviewsCited in 26 Documents MSC: 53C40 Global submanifolds Keywords:isoparametric hypersurfaces; principal curvatures Citations:Zbl 1143.53058; Zbl 1165.53032 PDF BibTeX XML Cite \textit{Q.-S. Chi}, Nagoya Math. J. 204, 1--18 (2011; Zbl 1243.53094) Full Text: DOI arXiv OpenURL References: [1] U. Abresch, Isoparametric hypersurfaces with four or six distinct principal curvatures , Math. Ann. 264 (1983), 283-302. · Zbl 0505.53027 [2] E. Cartan, Familles de surfaces isoparamétriques dans les espaces à courbure constante , Ann. Mat. Pura Appl. (4) 17 (1938), 177-191. · Zbl 0020.06505 [3] E. Cartan, Sur des familles remarquables d’hypersurfaces isoparamétriques dans les espaces sphériques , Math. Z. 45 (1939), 335-367. · Zbl 0021.15603 [4] E. 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