Journal of Mathematics

Volume 2013 (2013), Article ID 395787, 7 pages

http://dx.doi.org/10.1155/2013/395787

Research Article

Totally Contact Umbilical Lightlike Hypersurfaces of Indefinite -Manifolds

Rachna Rani,¹ Rakesh Kumar,² and R. K. Nagaich³

¹University College, Moonak, Punjab 148033, India

²University College of Engineering, Punjabi University, Patiala 147002, India

³Department of Mathematics, Punjabi University, Patiala 147002, India

Received 22 August 2012; Revised 5 November 2012; Accepted 8 November 2012

Academic Editor: Mingsheng Liu

Copyright © 2013 Rachna Rani et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

We study totally contact umbilical lightlike hypersurfaces of indefinite -manifolds and prove the nonexistence of totally contact umbilical lightlike hypersurface in indefinite -space form.

1. Introduction

The general theory of nondegenerate submanifolds of Riemannian or semi-Riemannian manifolds is one of the most important topics of differential geometry [1, 2]. But the theory of degenerate or lightlike submanifolds of semi-Riemannian manifolds is relatively new [3] and different due to the fact that their normal vector bundle intersects with the tangent bundle. Thus, the study of lightlike submanifolds becomes more difficult than the study of nondegenerate submanifolds and one cannot use, in the usual way, the classical theory of submanifold to define induced objects on a lightlike submanifold. The degenerate geometry rises within the semi-Riemannian context, due to the existence of causal character of geometrical objects: their spacelike, timelike, or lightlike nature implies the existence of three types of hypersurfaces and submanifolds.

A lightlike framed hypersurface of a Lorentz -manifold, with an induced metric connection, is a Killing horizon and a globally hyperbolic spacetime; a de Sitter spacetime can carry a framed structure [3, 4]. Moreover, the contact geometry has a significant use in differential equations, optics, and phase spaces of dynamical systems [5–7]. All these motivated us to study lightlike hypersurfaces of indefinite globally framed -manifold, in particular indefinite -manifolds.

In this paper, we study totally contact umbilical lightlike hypersurfaces of indefinite -manifolds and prove the nonexistence of totally contact umbilical lightlike hypersurface in indefinite -space form.

2. Preliminaries

A manifold of dimension is called a globally framed -manifold (-manifold) if it is endowed with a nowhere vanishing -tensor field of constant rank, such that is parallelizable; that is, there exist global vector fields , , with their dual -forms , satisfying

If the metric is a semi-Riemannian metric with index , such that

for any , accordingly is either spacelike or timelike, then the -manifold is called an indefinite metric -manifold. Then clearly , for any . An indefinite metric -manifold is called an indefinite -manifold if it is normal that is, the tensor field vanishes, where is Nijenhuis tensor of and , for any , where , for any . The Levi-Civita connection of an indefinite -manifold satisfies

where and . Also

and is integrable flat distribution, since , for detail see [8].

We recall notations and fundamental equations for lightlike hypersurfaces, which are due to Duggal and Bejancu [3].

Let be a -dimensional semi-Riemannian manifold with index , and let be a hypersurface of , with . is a lightlike hypersurface of if is of constant rank and the normal bundle is a distribution of rank on . A complementary bundle of in is a rank nondegenerate distribution over . It is denoted by and known as a screen distribution. Therefore we have

where is a orthogonal complementary vector bundle of in . The following theorem has important roles in studying the geometry of lightlike hypersurface.

Theorem 1. Let be a lightlike hypersurface of a semi-Riemannian manifold . Then there exists a unique vector bundle of rank over , such that for any nonzero section of on a coordinate neighborhood , there exists a unique section of on satisfying

Hence, we have the following decompositions of :

Let be the Levi-Civita connection on with respect to . Then using the decompositions in (7), Gauss and Weingarten formulae are given as

for any and , where and belong to while and belong to . Here is a torsion free linear connection on , is a -valued symmetric bilinear form on and known as the second fundamental form. is a linear operator on and known as the shape operator of lightlike immersion and is a linear connection on .

Locally, for the pair , following the Duggal and Bejancu's notation [3], we recall local second fundamental form and -form as

Hence locally, (8) becomes

If denotes the projection morphism of on then from (5), we have

for any , , where and belong to while and belong to . Here and are called the second fundamental form and the shape operator of the screen distribution, respectively. It should be noted that the induced linear connection is not a metric connection as it satisfies

where is a differential form locally defined on by . By direct calculation, we have

for any , , and . According to Duggal and Bejancu's notation [3], locally we have know

Then (11) become

and also give

From (9), it is clear that

that is, the second fundamental form of a lightlike hypersurface is degenerate. Following the notations of Duggal and Bejancu [3], for the curvature tensor of , we have , for any .

3. Lightlike Hypersurface of Indefinite -Manifolds

Let be a lightlike hypersurface of an indefinite -manifold , and such that the characteristic vector fields , are tangent to . As the ambient manifold has an additional geometric structure , we must look for a particular screen distribution on . Since , for any therefore is a distribution on of rank such that . Moreover , for any , therefore is tangent to . Since ; that is, the component of with respect to vanishes; this implies . As and are null vector fields satisfying , therefore from (2), we deduce that and are null vector fields satisfying . Hence is a vector subbundle of of rank . It is known [9] that if structure vector fields , are tangent to then belong to . Therefore implies that there exists a nondegenerate distribution of rank on such that

therefore

Let , and let then clearly is invariant and is anti-invariant under , and we have

Consider the local lightlike vector fields as

Using the decompositions in (21), any can be written as

where and are the projection morphisms of into and , respectively, and where , and is a local -form on defined by . Therefore

Applying to (23) and then using (24), we obtain . By assuming for any , we obtain a tensor field of type on and given by

Applying to (25) and then using the definition of , we obtain

Moreover, since therefore

for any . Thus we have the following theorem analogous to a theorem proved in [10].

Theorem 2. Let be an indefinite -manifold and let be a lightlike hypersurface of ; then is also a -manifold.

Since therefore applying to (26), we get , this implies that is an structure of constant rank on . Now using (2) and (25), we obtain

for any , where is a form locally defined on by . Replace by in (28) and using (26) and (27), we derive

Let be a lightlike hypersurface of an indefinite -manifold ; then by using (4), (10), and (25), we obtain

for any then comparing the tangential and transversal components, we get

Using (15) and (31), we get , taking inner product with , we get , and then using (29), we obtain

Using (3), for any , we get , therefore

4. Totally Contact Umbilical Lightlike Hypersurface of Indefinite -Manifolds

Here we will follow Bejancu's definition [11] of totally contact umbilical submanifolds of Sasakian manifolds to state totally contact umbilical lightlike hypersurfaces of indefinite -manifolds.

Definition 3. A lightlike hypersurface of an indefinite -manifold is said to be totally contact umbilical lightlike hypersurface if the second fundamental form of satisfies

for any , where is a transversal vector field on ; that is, , where is a smooth function on .

Remark 4. We can also write (35) as

where

and using (32)

for any . If , that is, ; then lightlike hypersurface is said to be totally contact geodesic.

Let be the curvature tensor fields of then for an indefinite -space form , we have (see [8])

for any , where and . Using (39), we obtain

Also, for the pair on , from (3.8) of page no. 94 of [3], we have

and , where

Hence using (40) and (41), we obtain

for any .

Lemma 5. Let be a totally contact umbilical lightlike hypersurface of an indefinite -manifold ; then for any , one has

Proof. By virtue of (37) and (42), we obtain

Now using (12) in (45), we have

Again using (12), we have

Thus from (46) and (47), the first expression of the theorem follows. Next, using (38) and (42), we obtain

Using (31) and (32), we get

and from (2), (3), (10), (16), (17), (18), and (25), we obtain

Thus by substituting (49) and (50) in (48), we obtain (44).

Theorem 6. Let be an indefinite -space form and be a totally contact umbilical lightlike hypersurface of . Then , where and satisfies the following differential equations:

for any .

Proof. Let be a totally contact umbilical lightlike hypersurface of an indefinite -space form of constant -sectional curvature . Then using (35), we have . Substituting (29), (44) in (43), we obtain

for any . Put in (52); we get

Put in (53) and then using , , ; we obtain

since , we get . Moreover, by putting and in (52), we obtain

Finally, putting , , and in (52) with and using that is nondegenerate, we obtain

Putting in (56), we get

By taking , we obtain

Since therefore using (19), we can write

where is an orthogonal basis of , then using (58), we have

which leads to get from (56)

Now, assume that there exists a vector field on some neighborhood of such that at some point in the neighborhood. Then from (61), it is clear that all the vectors of the fiber are collinear with . This contradicts . This implies the result.

From the previous mentioned theorem, we have the following corollary.

Corollary 7. There exist no totally contact umbilical lightlike real hypersurfaces of indefinite -space form    with .

Acknowledgment

The authors would like to thank the anonymous referee for his/her valuable suggestions that helped them to improve this paper.

References

B. Y. Chen, Geometry of Submanifolds, Marcel Dekker, New York, USA, 1973.

B. O’Neill, Semi-Riemannian Geometry with Applications to Relativity, Academic Press, 1983.

K. L. Duggal and A. Bejancu, Lightlike Submanifolds of Semi-Riemannian Manifolds and Applications, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1996.

K. L. Duggal and B. Sahin, “Lightlike submanifolds of indefinite Sasakian manifolds,” International Journal of Mathematics and Mathematical Sciences, vol. 2007, Article ID 57585, 21 pages, 2007.

V. I. Arnold, “Contact geometry: the geometrical method of Gibbss thermodynamics,” in Proceedings of the Gibbs Symposium, pp. 163–179, American Mathematical Society, New Haven, Conn, USA, 1989.

S. Maclane, Geometrical Mechanics II, Lecture Notes, University of Chicago, Chicago, Ill, USA, 1968.

V. E. Nazaikinskii, V. E. Shatalov, and B. Y. Sternin, Contact Geometry and Linear Differential Equations, vol. 6 of De Gruyter Expositions in Mathematics, Walter de Gruyter, Berlin, Germany, 1992.

L. Brunetti and A. M. Pastore, “Curvature of a class of indefinite globally framed f-manifolds,” Bulletin Mathematique de la Societe des Sciences Mathematiques de Roumanie, vol. 51, no. 3, pp. 183–204, 2008.

C. Calin, “On existence of degenerate hypersurfaces in Sasakian manifolds,” Arab Journal of Mathematical Sciences, vol. 5, pp. 21–27, 1999.

L. Brunetti and A. M. Pastore, “Lightlike hypersurfaces in indefiite -manifolds,” Differential Geometry—Dynamical Systems, vol. 12, pp. 18–40, 2010.

A. Bejancu, “Umbilical semi-invariant submanifolds of a Sasakian manifold,” Tensor, vol. 37, pp. 203–213, 1982.