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A basic inequality and new characterization of Whitney spheres in a complex space form

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Abstract

LetN n (4c) be ann-dimensional complex space form of constant holomorphic sectional curvature 4c and letx:M nN n (4c) be ann-dimensional Lagrangian submanifold inN n (4c). We prove that the following inequality always hold onM n:\(\left| {\bar \nabla h} \right|^2 \geqslant \frac{{3n^2 }}{{n + 2}}\left| {\nabla ^ \bot \vec H} \right|^2 \) whereh is the second fundamental form andH is the mean curvature of the submanifold. We classify all submanifolds which at every point realize the equality in the above inequality. As a direct consequence of our Theorem, we give, a new characterization of theWhitney spheres in a complex space form.

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Correspondence to Haizhong Li.

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Partially supported by a research fellowship of the Alexander von Humboldt Stiftung.

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Li, H., Vrancken, L. A basic inequality and new characterization of Whitney spheres in a complex space form. Isr. J. Math. 146, 223–242 (2005). https://doi.org/10.1007/BF02773534

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