Certain CR submanifolds of maximal CR dimension of complex space forms

We study m-dimensional real submanifolds with (m−1)-dimensional maximal holomorphic tangent subspace in complex space forms. On such a manifold there exists an almost contact structure which is naturally induced from the ambient space and in this paper we study the anti-commutative condition of the almost contact structure and the second fundamental form of these submanifolds and we characterize certain model spaces in complex space forms.     

Codimension reduction and second fundamental form of CR submanifolds in complex space forms

Considering n-dimensional real submanifolds M of a complex space form which are CR submanifolds of CR dimension , we study the condition h(FX,Y)+h(X,FY)=0 on the structure tensor F naturally induced from the almost complex structure J of the ambient manifold and on the second fundamental form h of submanifolds M.     

Isoparametric submanifolds in two-dimensional complex space forms

We show that an isoparametric submanifold of a complex hyperbolic plane, according to the definition of Heintze, Liu and Olmos’, is an open part of a principal orbit of a polar action. We also show that there exists a non-isoparametric submanifold of the complex hyperbolic plane that is isoparametric according to the definition of Terng’s. Finally, we classify Terng-isoparametric submanifolds of two-dimensional complex space forms.     

Pseudo-parallel Lagrangian submanifolds in complex space forms

In this work we study pseudo-parallel Lagrangian submanifolds in a complex space form. We give several general properties of pseudo-parallel submanifolds. For the 2-dimensional case, we show that any minimal Lagrangian surface is pseudo-parallel. We also give examples of non-minimal pseudo-parallel Lagrangian surfaces. Here we prove a local classification of the pseudo-parallel Lagrangian surfaces. In particular, semi-parallel Lagrangian surfaces are totally geodesic or flat. Finally, we give examples of pseudo-parallel Lagrangian surfaces which are not semi-parallel.     

Biminimal Lagrangian H-umbilical submanifolds in complex space forms

All biminimal Lagrangian surfaces of nonzero constant mean curvature in 2-dimensional complex space forms have been determined in Sasahara (Differ Geom Appl 27:647?C652, 2009). In this paper, we completely determine biminimal Lagrangian H-umbilical submanifolds of nonzero constant mean curvature in complex space forms of dimension ?? 3.     

Gap theorems for Lagrangian submanifolds in complex space forms

Geometriae Dedicata - Inspired by a recent work of Grove and Petersen (Alexandrov spaces with maximal radius, 2018), where the authors studied positively curved Alexandrov spaces with largest...     

不定复空间形式的极小Lagrangian子流形

确定了所有不定复空间形式中立方形式具有SO(k-1,n-k)或SO(k,n-k-1)对称性的极小Lagrangian子流形.     

The scalar curvature of CR submanifolds of maximal CR dimension of complex projective space

We treat n-dimensional compact minimal submanifolds of complex projective space when the maximal holomorphic tangent subspace is (n − 1)-dimensional and we give a sufficient condition for such submanifolds to be tubes over totally geodesic complex subspaces. Authors’ addresses: Mirjana Djorić, Faculty of Mathematics, University of Belgrade, Studentski trg 16, pb. 550, 11000 Belgrade, Serbia; Masafumi Okumura, 5-25-25 Minami Ikuta, Tama-ku, Kawasaki, Japan     

Normal curvature of CR submanifolds of maximal CR dimension of the complex projective space

We prove that there do not exist CR submanifolds Mⁿ of maximal CR dimension of a complex projective space \({\mathbf{P}^{\frac{n+p}{2}}(\mathbf{C})}\) with flat normal connection D of M, when the distinguished normal vector field is parallel with respect to D. If D is lift-flat, then there exists a totally geodesic complex projective subspace \({\mathbf{P}^{\frac{n+1}{2}}(\mathbf{C})}\) of \({\mathbf{P}^{\frac{n+p}{2}}(\mathbf{C})}\) such that M is a real hypersurface of \({\mathbf{P}^{\frac{n+1}{2}}(\mathbf{C})}\).     

Optimal general inequalities for Lagrangian submanifolds in complex space forms

Lagrangian submanifolds appear naturally in the context of classical mechanics. Moreover, they play some important roles in supersymmetric field theories as well as in string theory. In this paper we establish general inequalities for Lagrangian submanifolds in complex space forms. We also provide examples showing that these inequalities are the best possible. Moreover, we provide simple non-minimal examples which satisfy the equality case of the improved inequalities.     

Classification of Casorati ideal Lagrangian submanifolds in complex space forms

In this paper, using optimization methods on Riemannian submanifolds, we establish two improved inequalities for generalized normalized δ-Casorati curvatures of Lagrangian submanifolds in complex space forms. We provide examples showing that these inequalities are the best possible and classify all Casorati ideal Lagrangian submanifolds (in the sense of B.-Y. Chen) in a complex space form. In particular, we generalize the recent results obtained in G.E. Vîlcu (2018) [34].     

Completeness of curvature surfaces of submanifolds in complex space forms

We assume that on an open subset of a submanifold M of an arbitrary Riemannian ambient space N the eigenspaces of the shape operator of M induce a foliation L whose leaves are spherical submanifolds of N. In this situation we derive a condition which characterizes when the leaves of L are complete Riemannian submanifolds of M (see Theorem 2.4). We apply this result to real hypersurfaces of complex space forms, in particular Hopf hypersurfaces (see Theorem 3.2 and Proposition 3.3).     

Compact submanifolds in space forms

We use closed conformal vector fields in a constant sectional curvature Riemannian manifold ${\mathbb{M}}$ to study the geometry of its immersed submanifolds. In this situation we obtain a characterization of sphere among compact submanifolds with positive Ricci curvature immersed in ${\mathbb{M}}$ .     

Conformally flat,minimal, Lagrangian submanifolds in complex space forms

We investigate n-dimensional (n ⩾ 4), conformally flat, minimal, Lagrangian submanifolds of the n-dimensional complex space form in terms of the multiplicities of the eigenvalues of the Schouten tensor and classify those that admit at most one eigenvalue of multiplicity one. In the case where the ambient space is ℂⁿ, the quasi umbilical case was studied in Blair (2007). However, the classification there is not complete and several examples are missing. Here, we complete (and extend) the classification and we also deal with the case where the ambient complex space form has non-vanishing holomorphic sectional curvature.