CR-lightlike submanifolds of a golden semi-Riemannian manifold are the focus of the research presented in this work, which aims to define and investigate these structures. Under the context of a golden semi-Riemannian manifold, we study the properties of geodesic CR-lightlike submanifolds as well as umbilical CR-lightlike submanifolds. In addition, on a golden semi-Riemannian manifold, we find numerous intriguing findings for entirely geodesic and totally umbilical CR-lightlike subamnifolds. Also, we construct an example of a CR-lightlike submanifold of a golden semi-Riemannian manifold.
Citation: Mohammad Aamir Qayyoom, Rawan Bossly, Mobin Ahmad. On CR-lightlike submanifolds in a golden semi-Riemannian manifold[J]. AIMS Mathematics, 2024, 9(5): 13043-13057. doi: 10.3934/math.2024636
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CR-lightlike submanifolds of a golden semi-Riemannian manifold are the focus of the research presented in this work, which aims to define and investigate these structures. Under the context of a golden semi-Riemannian manifold, we study the properties of geodesic CR-lightlike submanifolds as well as umbilical CR-lightlike submanifolds. In addition, on a golden semi-Riemannian manifold, we find numerous intriguing findings for entirely geodesic and totally umbilical CR-lightlike subamnifolds. Also, we construct an example of a CR-lightlike submanifold of a golden semi-Riemannian manifold.
The concept of lightlike submanifolds in geometry was initially established and expounded upon in a work produced by Duggal and Bejancu [1]. A nondegenerate screen distribution was employed in order to produce a nonintersecting lightlike transversal vector bundle of the tangent bundle. They defined the CR-lightlike submanifold as a generalization of lightlike real hypersurfaces of indefinite Kaehler manifolds and showed that CR-lightlike submanifolds do not contain invariant and totally real lightlike submanifolds. Further, they defined and studied GCR-lightlike submanifolds of Kaehler manifolds as an umbrella of invariant submanifolds, screen real submanifolds, and CR-lightlike and SCR-lightlike submanifolds in [2,3], respectively. Subsequently, B. Sahin and R. Gunes investigated geodesic property of CR-lightlike submanifolds [4] and the integrability of distributions in CR-lightlike submanifolds [5]. In the year 2010, Duggal and Sahin published a book [6]pertaining to the field of differential geometry, specifically focusing on the study of lightlike submanifolds. This book provides a comprehensive examination of recent advancements in lightlike geometry, encompassing novel geometric findings, accompanied by rigorous proofs, and exploring their practical implications in the field of mathematical physics. The investigation of the geometric properties of lightlike hypersurfaces and lightlike submanifolds has been the subject of research in several studies (see [7,8,9,10,11,12,13,14]).
Crasmareanu and Hretcanu[15] created a special example of polynomial structure [16] on a differentiable manifold, and it is known as the golden structure (¯M,g). Hretcanu C. E. [17] explored Riemannian submanifolds with the golden structure. M. Ahmad and M. A. Qayyoom studied geometrical properties of Riemannian submanifolds with golden structure [18,19,20,21] and metallic structure [22,23]. The integrability of golden structures was examined by A. Gizer et al. [24]. Lightlike hypersurfaces of a golden semi-Riemannian manifold was investigated by N. Poyraz and E. Yasar [25]. The golden structure was also explored in the studies [26,27,28,29].
In this research, we investigate the CR-lightlike submanifolds of a golden semi-Riemannian manifold, drawing inspiration from the aforementioned studies. This paper has the following outlines: Some preliminaries of CR-lightlike submanifolds are defined in Section 2. We establish a number of properties of CR-lightlike submanifolds on golden semi-Riemannian manifolds in Section 3. In Section 4, we look into several CR-lightlike submanifolds characteristics that are totally umbilical. We provide a complex illustration of CR-lightlike submanifolds of a golden semi-Riemannian manifold in the final section.
Assume that (¯ℵ,g) is a semi-Riemannian manifold with (k+j)-dimension, k,j≥1, and g as a semi-Riemannian metric on ¯ℵ. We suppose that ¯ℵ is not a Riemannian manifold and the symbol q stands for the constant index of g.
[15] Let ¯ℵ be endowed with a tensor field ψ of type (1,1) such that
ψ2=ψ+I, | (2.1) |
where I represents the identity transformation on Γ(Υ¯ℵ). The structure ψ is referred to as a golden structure. A metric g is considered ψ-compatible if
g(ψγ,ζ)=g(γ,ψζ) | (2.2) |
for all γ, ζ vector fields on Γ(Υ¯ℵ), then (¯ℵ,g,ψ) is called a golden Riemannian manifold. If we substitute ψγ into γ in (2.2), then from (2.1) we have
g(ψγ,ψζ)=g(ψγ,ζ)+g(γ,ζ). | (2.3) |
for any γ,ζ∈Γ(Υ¯ℵ).
If (¯ℵ,g,ψ) is a golden Riemannian manifold and ψ is parallel with regard to the Levi-Civita connection ¯∇ on ¯ℵ:
¯∇ψ=0, | (2.4) |
then (¯ℵ,g,ψ) is referred to as a semi-Riemannian manifold with locally golden properties.
The golden structure is the particular case of metallic structure [22,23] with p=1, q=1 defined by
ψ2=pψ+qI, |
where p and q are positive integers.
[1] Consider the case where ℵ is a lightlike submanifold of k of ¯ℵ. There is the radical distribution, or Rad(Υℵ), on ℵ that applies to this situation such that Rad(Υℵ)=Υℵ∩Υℵ⊥, ∀ p∈ℵ. Since RadΥℵ has rank r≥0, ℵ is referred to as an r-lightlike submanifold of ¯ℵ. Assume that ℵ is a submanifold of ℵ that is r-lightlike. A screen distribution is what we refer to as the complementary distribution of a Rad distribution on Υℵ, then
Υℵ=RadΥℵ⊥S(Υℵ). |
As S(Υℵ) is a nondegenerate vector sub-bundle of Υ¯ℵ|ℵ, we have
Υ¯ℵ|ℵ=S(Υℵ)⊥S(Υℵ)⊥, |
where S(Υℵ)⊥ consists of the orthogonal vector sub-bundle that is complementary to S(Υℵ) in Υ¯ℵ|ℵ. S(Υℵ),S(Υℵ⊥) is an orthogonal direct decomposition, and they are nondegenerate.
S(Υℵ)⊥=S(Υℵ⊥)⊥S(Υℵ⊥)⊥. |
Let the vector bundle
tr(Υℵ)=ltr(Υℵ)⊥S(Υℵ⊥). |
Thus,
Υ¯ℵ=Υℵ⊕tr(Υℵ)=S(Υℵ)⊥S(Υℵ⊥)⊥(Rad(Υℵ)⊕ltr(Υℵ). |
Assume that the Levi-Civita connection is ¯∇ on ¯ℵ. We have
¯∇γζ=∇γζ+h(γ,ζ),∀γ,ζ∈Γ(Υℵ) | (2.5) |
and
¯∇γζ=−Ahζ+∇⊥γh,∀γ∈Γ(Υℵ)andh∈Γ(tr(Υℵ)), | (2.6) |
where {∇γζ,Ahγ} and {h(γ,ζ),∇⊥γh} belongs to Γ(Υℵ) and Γ(tr(Υℵ)), respectively.
Using projection L:tr(Υℵ)→ltr(Υℵ), and S:tr(Υℵ)→S(Υℵ⊥), we have
¯∇γζ=∇γζ+hl(γ,ζ)+hs(γ,ζ), | (2.7) |
¯∇γℵ=−Aℵγ+∇lγℵ+λs(γ,ℵ), | (2.8) |
and
¯∇γχ=−Aχγ+∇sγ+λl(γ,χ) | (2.9) |
for any γ,ζ∈Γ(Υℵ),ℵ∈Γ(ltr(Υℵ)), and χ∈Γ(S(Υℵ⊥)), where hl(γ,ζ)=Lh(γ,ζ),hs(γ,ζ)=Sh(γ,ζ),∇lγℵ,λl(γ,χ)∈Γ(ltr(Tℵ)),∇sγλs(γ,ℵ)∈Γ(S(Υℵ⊥)), and ∇γζ,Aℵγ,Aχγ∈Γ(Υℵ).
The projection morphism of Υℵ on the screen is represented by P, and we take the distribution into consideration.
∇γPζ=∇∗γPζ+h∗(γ,Pζ),∇γξ=−A∗ξγ+∇∗tγξ, | (2.10) |
where γ,ζ∈Γ(Υℵ),ξ∈Γ(Rad(Υℵ)).
Thus, we have the subsequent equation.
g(h∗(γ,Pζ),ℵ)=g(Aℵγ,Pζ), | (2.11) |
Consider that ¯∇ is a metric connection. We get
(∇γg)(ζ,η)=g(hl(γ,ζ),η)+g(hl(γ,ζη),ζ). | (2.12) |
Using the characteristics of a linear connection, we can obtain
(∇γhl)(ζ,η)=∇lγ(hl(ζ,η))−hl(¯∇γζ,η)−hl(ζ,¯∇γη), | (2.13) |
(∇γhs)(ζ,η)=∇sγ(hs(ζ,η))−hs(¯∇γζ,η)−hs(ζ,¯∇γη). | (2.14) |
Based on the description of a CR-lightlike submanifold in [4], we have
Υℵ=λ⊕λ′, |
where λ=Rad(Υℵ)⊥ψRad(Υℵ)⊥λ0.
S and Q stand for the projection on λ and λ′, respectively, then
ψγ=fγ+wγ |
for γ,ζ∈Γ(Υℵ), where fγ=ψSγ and wγ=ψQγ.
On the other hand, we have
ψζ=Bζ+Cζ |
for any ζ∈Γ(tr(Υℵ)), Bζ∈Γ(Υℵ) and Cζ∈Γ(tr(Υℵ)), unless ℵ1 and ℵ2 are denoted as ψL1 and ψL2, respectively.
Lemma 2.1. Assume that the screen distribution is totally geodesic and that ℵ is a CR-lightlike submanifold of the golden semi-Riemannian manifold, then ∇γζ∈Γ(S(ΥN)), where γ,ζ∈Γ(S(Υℵ)).
Proof. For γ,ζ∈Γ(S(Υℵ)),
g(∇γζ,ℵ)=g(¯∇γζ−h(γ,ζ),ℵ)=−g(ζ,¯∇γℵ). |
Using (2.8),
g(∇γζ,ℵ)=−g(ζ,−Aℵγ+∇⊥γℵ)=g(ζ,Aℵγ). |
Using (2.11),
g(∇γζ,ℵ)=g(h∗(γ,ζ),ℵ). |
Since screen distribution is totally geodesic, h∗(γ,ζ)=0,
g(¯∇γζ,ℵ)=0. |
Using Lemma 1.2 in [1] p.g. 142, we have
∇γζ∈Γ(S(Υℵ)), |
where γ,ζ∈Γ(S(Υℵ)).
Theorem 2.2. Assume that ℵ is a locally golden semi-Riemannian manifold ¯ℵ with CR-lightlike properties, then ∇γψγ=ψ∇γγ for γ∈Γ(λ0).
Proof. Assume that γ,ζ∈Γ(λ0). Using (2.5), we have
g(∇γψγ,ζ)=g(¯∇γψγ−h(γ,ψγ),ζ)g(∇γψγ,ζ)=g(ψ(¯∇γγ),ζ)g(∇γψγ,ζ)=g(ψ(∇γγ),ζ),g(∇γψγ−ψ(∇γγ),ζ)=0. |
Nondegeneracy of λ0 implies
∇γψγ=ψ(∇γγ), |
where γ∈Γ(λ0).
Definition 3.1. [4] A CR-lightlike submanifold of a golden semi-Riemannian manifold is mixed geodesic if h satisfies
h(γ,α)=0, |
where h stands for second fundamental form, γ∈Γ(λ), and α∈Γ(λ′).
For γ,ζ∈Γ(λ) and α,β∈Γ(λ′) if
h(γ,ζ)=0 |
and
h(α,β)=0, |
then it is known as λ-geodesic and λ′-geodesic, respectively.
Theorem 3.2. Assume ℵ is a CR-lightlike submanifold of ¯ℵ, which is a golden semi-Riemannian manifold. ℵ is totally geodesic if
(Lg)(γ,ζ)=0 |
and
(Lχg)(γ,ζ)=0 |
for α,β∈Γ(Υℵ),ξ∈Γ(Rad(Υℵ)), and χ∈Γ(S(Υℵ⊥)).
Proof. Since ℵ is totally geodesic, then
h(γ,ζ)=0 |
for γ,ζ∈Γ(Υℵ).
We know that h(γ,ζ)=0 if
g(h(γ,ζ),ξ)=0 |
and
g(h(γ,ζ),χ)=0. |
g(h(γ,ζ),ξ)=g(¯∇γζ−∇γζ,ξ)=−g(ζ,[γ,ξ]+¯∇ξγ=−g(ζ,[γ,ξ])+g(γ,[ξ,ζ])+g(¯∇ζξ,γ)=−(Lξg)(γ,ζ)+g(¯∇ζξ,γ)=−(Lξg)(γ,ζ)−g(ξ,h(γ,ζ)))2g(h(γ,ζ)=−(Lξg)(γ,ζ). |
Since g(h(γ,ζ),ξ)=0, we have
(Lξg)(γ,ζ)=0. |
Similarly,
g(h(γ,ζ),χ)=g(¯∇γζ−∇γζ,χ)=−g(ζ,[γ,χ])+g(γ,[χ,ζ])+g(¯∇ζχ,γ)=−(Lχg)(γ,ζ)+g(¯∇ζχ,γ)2g(h(γ,ζ),χ)=−(Lχg)(γ,ζ). |
Since g(h(γ,ζ),χ)=0, we get
(Lχg)(γ,ζ)=0 |
for χ∈Γ(S(Υℵ⊥)).
Lemma 3.3. Assume that ¯ℵ is a golden semi-Riemannian manifold whose submanifold ℵ is CR-lightlike, then
g(h(γ,ζ),χ)=g(Aχγ,ζ) |
for γ∈Γ(λ),ζ∈Γ(λ′) and χ∈Γ(S(Υℵ⊥)).
Proof. Using (2.5), we get
g(h(γ,ζ),χ)=g(¯∇γζ−∇γζ,χ)=g(ζ,¯∇γχ). |
From (2.9), it follows that
g(h(γ,ζ),χ)=−g(ζ,−Aχγ+∇sγχ+λs(γ,χ))=g(ζ,Aχγ)−g(ζ,∇sγχ)−g(ζ,λs(γ,χ))g(h(γ,ζ),χ)=g(ζ,Aχγ), |
where γ∈Γ(λ),ζ∈Γ(λ′),χ∈Γ(S(Υℵ⊥)).
Theorem 3.4. Assume that ℵ is a CR-lightlike submanifold of the golden semi-Riemannian manifold and ¯ℵ is mixed geodesic if
A∗ξγ∈Γ(λ0⊥ψL1) |
and
Aχγ∈Γ(λ0⊥Rad(Υℵ)⊥ψL1) |
for γ∈Γ(λ),ξ∈Γ(Rad(Υℵ)), and χ∈Γ(S(Υℵ⊥)).
Proof. For γ∈Γ(λ),ζ∈Γ(λ′), and χ∈Γ(S(Υℵ⊥)), we get
Using (2.5),
g(h(γ,ζ),ξ)=g(¯∇γζ−∇γζ,ξ)=−g(ζ,¯∇γξ). |
Again using (2.5), we obtain
g(h(γ,ζ),ξ)=−g(ζ,∇γξ+h(γ,ξ))=−g(ζ,∇γξ). |
Using (2.10), we have
g(h(γ,ζ),ξ)=−g(ζ,−A∗ξγ+∇∗tγξ)g(ζ,A∗ξγ)=0. |
Since the CR-lightlike submanifold ℵ is mixed geodesic, we have
g(h(γ,ζ),ξ)=0 |
⇒g(ζ,A∗ξγ)=0 |
⇒A∗ξγ∈Γ(λ0⊥ψL1), |
where γ∈Γ(λ),ζ∈Γ(λ′).
From (2.5), we get
g(h(γ,ζ),χ)=g(¯∇γζ−∇γζ,χ)=−g(ζ,¯∇γχ). |
From (2.9), we get
g(h(γ,ζ),χ)=−g(ζ,−Aχγ+∇sγχ+λl(γ,χ))g(h(γ,ζ),χ)=g(ζ,Aχγ). |
Since, ℵ is mixed geodesic, then g(h(γ,ζ),χ)=0
⇒g(ζ,Aχγ)=0. |
Aχγ∈Γ(λ0⊥Rad(Υℵ)⊥ψ1). |
Theorem 3.5. Suppose that ℵ is a CR-lightlike submanifold of a golden semi-Riemannian manifold ¯ℵ, then ℵ is λ′-geodesic if Aχη and A∗ξη have no component in ℵ2⊥ψRad(Υℵ) for η∈Γ(λ′),ξ∈Γ(Rad(Υℵ)), and χ∈Γ(S(Υℵ⊥)).
Proof. From (2.5), we obtain
g(h(η,β),χ)=g(¯∇ηβ−∇γζ,χ)=−¯g(∇γζ,χ), |
where χ,β∈Γ(λ′).
Using (2.9), we have
g(h(η,β),χ)=−g(β,−Aχη+∇sη+λl(η,χ))g(h(η,β),χ)=g(β,Aχη). | (3.1) |
Since ℵ is λ′-geodesic, then g(h(η,β),χ)=0.
From (3.1), we get
g(β,Aχη)=0. |
Now,
g(h(η,β),ξ)=g(¯∇ηβ−∇ηβ,ξ)=g(¯∇ηβ,ξ)=−g(β,¯∇ηξ). |
From (2.10), we get
g(h(η,β),ξ)=−g(η,−A∗ξη+∇∗tηξ)g(h(η,β),ξ)=g(A∗ξβ,η). |
Since ℵ is λ′- geodesic, then
g(h(η,β),ξ)=0 |
⇒g(A∗ξβ,η)=0. |
Thus, Aχη and A∗ξη have no component in M2⊥ψRad(Υℵ).
Lemma 3.6. Assume that ¯ℵ is a golden semi-Riemannian manifold that has a CR-lightlike submanifold ℵ. Due to the distribution's integrability, the following criteria hold.
(ⅰ) ψg(λl(ψγ,χ),ζ)−g(λl(γ,χ),ψζ)=g(Aχψγ,ζ)−g(Aχγ,ψζ),
(ⅱ) g(λl(ψγ),ξ)=g(Aχγ,ψξ),
(ⅲ) g(λl(γ,χ),ξ)=g(Aχψγ,ψξ)−g(Aχγ,ψξ),
where γ,ζ∈Γ(Υℵ),ξ∈Γ(Rad(Υℵ)), and χ∈Γ(S(Υℵ⊥)).
Proof. From Eq (2.9), we obtain
g(λl(ψγ,χ),ζ)=g(¯∇ψγχ+Aχψγ−∇sψγχ,ζ)=−g(χ,¯∇ψγζ)+g(Aχψγ,ζ). |
Using (2.5), we get
g(λl(ψγ,χ),ζ)=−g(χ,∇ψγζ+h(ψγ,ζ))+g(Aχψγ,ζ)=−g(χ,h(γ,ψζ))+g(Aχψγ,ζ). |
Again, using (2.5), we get
g(λl(ψγ,χ),ζ)=−g(χ,¯∇γψζ−∇γψζ)+g(Aχψγ,ζ)=g(¯∇γχ,ψζ)+g(Aχψγ,ζ). |
Using (2.9), we have
g(λl(ψγ,χ),ζ)=g(−Aχγ+∇sγχ+λl(γ,χ),ψζ)+g(λl(ψγ,χ),ζ)−g(λl(γ,χ),ψζ)=g(Aχψγ,ζ)−g(Aχγ,ψζ). |
(ⅱ) Using (2.9), we have
g(λl(ψγ,χ),ξ)=g(Aχψγ−∇sψγχ+∇ψγχ,ξ)=g(Aχψγ,ξ)−g(χ,¯∇ψγξ). |
Using (2.10), we get
g(λl(ψγ,χ),ξ)=g(Aχψγ,ξ)+g(χ,A∗ξψγ)−g(χ,∇∗tψγ,ξ)g(λl(ψγ),ξ)=g(Aχγ,ψξ). |
(ⅲ) Replacing ζ by ψξ in (ⅰ), we have
ψg(λl(ψγ,χ),ψξ)−g(λl(γ,χ),ψ2ξ)=g(Aχψγ,ψξ)−g(Aχγ,ψ2ξ). |
Using Definition 2.1 in [18] p.g. 9, we get
ψg(λl(ψγ,χ),ψξ)−g(λl(γ,χ),(ψ+I)ξ)=g(Aχψγ,ψξ)−g(Aχγ,(ψ+I)ξ)ψg(λl(ψγ,χ),ψξ)−g(λl(γ,χ),ψξ)−g(λl(γ,χ),ξ)=g(Aχψγ,ψξ)−g(Aχγ,ψξ)−g(Aχγ,ξ).g(λl(γ,χ),ξ)=g(Aχψγ,ψξ)−g(Aχγ,ψξ). |
Definition 4.1. [12] A CR-lightlike submanifold of a golden semi-Riemannian manifold is totally umbilical if there is a smooth transversal vector field H∈tr Γ(Υℵ) that satisfies
h(χ,η)=Hg(χ,η), |
where h is stands for second fundamental form and χ, η∈ Γ(Υℵ).
Theorem 4.2. Assume that the screen distribution is totally geodesic and that ℵ is a totally umbilical CR-lightlike submanifold of the golden semi-Riemannian manifold ¯ℵ, then
Aψηχ=Aψχη,∀χ,η∈Γλ′. |
Proof. Given that ¯ℵ is a golden semi-Riemannian manifold,
ψ¯∇ηχ=¯∇ηψχ. |
Using (2.5) and (2.6), we have
ψ(∇ηχ)+ψ(h(η,χ))=−Aψχη+∇tηψχ. | (4.1) |
Interchanging η and χ, we obtain
ψ(∇χη)+ψ(h(χ,η))=−Aψηχ+∇tχψη. | (4.2) |
Subtracting Eqs (4.1) and (4.2), we get
ψ(∇ηχ−∇χη)−∇tηψχ+∇tχψη=Aψηχ−Aψχη. | (4.3) |
Taking the inner product with γ∈Γ(λ0) in (4.3), we have
g(ψ(∇χη,γ)−g(ψ(∇χη,γ)=g(Aψηχ,γ)−g(Aψχη,γ).g(Aψηχ−Aψχη,γ)=g(∇χη,−ψγ)g(∇χη,ψγ). | (4.4) |
Now,
g(∇χη,ψγ)=g(¯∇χη−h(χ,η),ψγ)g(∇χη,ψγ)=−g(η,(¯∇χψ)γ−ψ(¯∇χγ)). |
Since ψ is parallel to ¯∇, i.e., ¯∇γψ=0,
g(∇χη,ψγ)=−ψ(¯∇χγ)). |
Using (2.7), we have
g(∇χη,ψγ)=−g(ψη,∇χγ+hs(χ,γ)+hl(χ,γ))g(∇χη,ψγ)=−g(ψη,∇χγ)−g(ψη,hs(χ,γ))−g(ψη,hl(χ,γ)). | (4.5) |
Since ℵ is a totally umbilical CR-lightlike submanifold and the screen distribution is totally geodesic,
hs(χ,γ)=Hsg(χ,γ)=0 |
and
hl(χ,γ)=Hlg(χ,γ)=0, |
where χ∈Γ(λ′) and γ∈Γ(λ0).
From (4.5), we have
g(∇χη,ψγ)=−g(ψη,∇χγ). |
From Lemma 2.1, we get
g(∇χη,ψγ)=0. |
Similarly,
g(∇ηχ,ψγ)=0 |
Using (4.4), we have
g(Aψηχ−Aψχη,γ)=0. |
Since λ0 is nondegenerate,
Aψηχ−Aψχη=0 |
⇒Aψηχ=Aψχη. |
Theorem 4.3. Let ℵ be the totally umbilical CR-lightlike submanifold of the golden semi-Riemannian manifold ¯ℵ. Consequently, ℵ's sectional curvature, which is CR-lightlike, vanishes, resulting in ¯K(π)=0, for the entire CR-lightlike section π.
Proof. We know that ℵ is a totally umbilical CR-lightlike submanifold of ¯ℵ, then from (2.13) and (2.14),
(∇γhl)(ζ,ω)=g(ζ,ω)∇lγHl−Hl{(∇γg)(ζ,ω)}, | (4.6) |
(∇γhs)(ζ,ω)=g(ζ,ω)∇sγHs−Hs{(∇γg)(ζ,ω)} | (4.7) |
for a CR-lightlike section π=γ∧ω,γ∈Γ(λ0),ω∈Γ(λ′).
From (2.12), we have (∇Ug)(ζ,ω)=0. Therefore, from (4.6) and (4.7), we get
(∇γhl)(ζ,ω)=g(ζ,ω)∇lγHl, | (4.8) |
(∇γhs)(ζ,ω)=g(ζ,ω)∇sγHs. | (4.9) |
Now, from (4.8) and (4.9), we get
{¯R(γ,ζ)ω}tr=g(ζ,ω)∇lγHl−g(γ,ω)∇lζHl+g(ζ,ω)λl(γ,Hs)−g(γ,ω)λl(ζ,Hs)+g(ζ,ω)∇sγHs−g(γ,ω)∇sζHs+g(ζ,ω)λs(γ,Hl)−g(γ,ω)λs(ζ,Hl). | (4.10) |
For any β∈Γ(tr(Υℵ)), from Equation (4.10), we get
¯R(γ,ζ,ω,β)=g(ζ,ω)g(∇lγHl,β)−g(γ,ω)g(∇lζHl,β)+g(ζ,ω)g(λl(γ,Hs),ζ)−g(γ,ω)g(λl(ζ,Hs),β)+g(ζ,ω)g(∇sγHs,β)−g(γ,ω)g(∇sζHs,β)+g(ζ,ω)g(λs(γ,Hl),β)−g(γ,ω)g(λs(ζ,Hl,β). |
R(γ,ω,ψγ,ψω)=g(ω,ψγ)g(∇lγHl,ψω)−g(γ,ψγ)g(∇lωHl,ψω)+g(ω,ψγ)g(λl(γ,Hs),ψω)−g(γ,ψγ)g(λl(ω,Hs),ψω)+g(ω,ψγ)g(∇sγHs,ψω)−g(γ,ψγ)g(∇sωHs,ψω)+g(ω,ψγ)g(λs(γ,Hl),ψω)−g(γ,ψγ)g(λs(ω,Hl,ψU). |
For any unit vectors γ∈Γ(λ) and ω∈Γ(λ′), we have
¯R(γ,ω,ψγ,ψω)=¯R(γ,ω,γ,ω)=0. |
We have
K(γ)=KN(γ∧ζ)=g(¯R(γ,ζ)ζ,γ), |
where
¯R(γ,ω,γ,ω)=g(¯R(γ,ω)γ,ω) |
or
¯R(γ,ω,ψγ,ψω)=g(¯R(γ,ω)ψγ,ψω) |
i.e.,
¯K(π)=0 |
for all CR-sections π.
Example 5.1. We consider a semi-Riemannian manifold R62 and a submanifold ℵ of co-dimension 2 in R62, given by equations
υ5=υ1cosα−υ2sinα−υ3z4tanα, |
υ6=υ1sinα−υ2cosα−υ3υ4, |
where α∈R−{π2+kπ; k∈z}. The structure on R62 is defined by
ψ(∂∂υ1,∂∂υ2,∂∂υ3,∂∂υ4,∂∂υ5,∂∂υ6)=(¯ϕ ∂∂υ1,¯ϕ∂∂υ2,ϕ∂∂υ3,ϕ∂∂υ4,ϕ∂∂υ5,ϕ∂∂υ6). |
Now,
ψ2(∂∂υ1,∂∂υ2,∂∂υ3,∂∂υ4,∂∂υ5,∂∂υ6)=((¯ϕ+1) ∂∂υ1,(¯ϕ+1)∂∂υ2,(ϕ+1)∂∂υ3,(ϕ+1)∂∂υ4, |
(ϕ+1)∂∂υ5,(ϕ+1)∂∂υ6) |
ψ2=ψ+I. |
It follows that (R62,ψ) is a golden semi-Reimannian manifold.
The tangent bundle Υℵ is spanned by
Z0=−sinα ∂∂υ5−cosα ∂∂υ6−ϕ ∂∂υ2, |
Z1=−ϕ sinα ∂∂υ5−ϕ cosα ∂∂υ6+ ∂∂υ2, |
Z2=∂∂υ5−¯ϕ sinα ∂∂υ2+∂∂υ1, |
Z3=−¯ϕ cosα ∂∂υ2+∂∂υ4+i∂∂υ6. |
Thus, ℵ is a 1-lightlike submanifold of R62 with RadΥℵ=Span{X0}. Using golden structure of R62, we obtain that X1=ψ(X0). Thus, ψ(RadΥℵ) is a distribution on ℵ. Hence, the ℵ is a CR-lightlike submanifold.
In general relativity, particularly in the context of the black hole theory, lightlike geometry finds its uses. An investigation is made into the geometry of the ℵ golden semi-Riemannian manifolds that are CR-lightlike in nature. There are many intriguing findings on completely umbilical and completely geodesic CR-lightlike submanifolds that are examined. We present a required condition for a CR-lightlike submanifold to be completely geodesic. Moreover, it is demonstrated that the sectional curvature K of an entirely umbilical CR-lightlike submanifold ℵ of a golden semi-Riemannian manifold ¯ℵ disappears.
The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.
The present work (manuscript number IU/R&D/2022-MCN0001708) received financial assistance from Integral University in Lucknow, India as a part of the seed money project IUL/IIRC/SMP/2021/010. All of the authors would like to express their gratitude to the university for this support. The authors are highly grateful to editors and referees for their valuable comments and suggestions for improving the paper. The present manuscript represents the corrected version of preprint 10.48550/arXiv.2210.10445. The revised version incorporates the identities of all those who have made contributions, taking into account their respective skills and understanding.
Authors have no conflict of interests.
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