FUNDAMENTALNAYA I PRIKLADNAYA MATEMATIKA

(FUNDAMENTAL AND APPLIED MATHEMATICS)

2002, VOLUME 8, NUMBER 2, PAGES 357-364

On the type number of nearly-cosymplectic hypersurfaces in nearly-Kählerian manifolds

M. B. Banaru

Abstract

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Nearly-cosymplectic hypersurfaces in nearly-K\"ahlerian manifolds are considered. The following results are obtained.

\textbf{Theorem 1.} The type number of a nearly-cosymplectic hypersurface in a nearly-K\"ahlerian manifold is at most one.

\textbf{Theorem 2.} Let $\sigma$ be the second fundamental form of the immersion of a nearly-cosymplectic hypersurface $(N,\{\Phi,\xi,\eta,g\})$ in a nearly-K\"ahlerian manifold $M^{2n}$. Then $N$ is a minimal submanifold of $M^{2n}$ if and only if $\sigma(\xi,\xi) = 0$.

\textbf{Theorem 3.} Let $N$ be a nearly-cosymplectic hypersurface in a nearly-K\"ahlerian manifold $M^{2n}$, and let $T$ be its type number. Then the following statements are equivalent:

1) $N$ is a minimal submanifold of $M^{2n}$;

2) $N$ is a totally geodesic submanifold of $M^{2n}$;

3) $T \equiv 0$.

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Last modified: November 26, 2002