We consider the non-resonance with one-sided superlinear growth conditions for the indefinite planar system z′=f(t,z) from a rotation number viewpoint, and obtain the existence of 2π-periodic solutions by applying a rotation number approach together with the Poincaré-Bohl theorem. We allow that the angular velocity of solutions of z′=f(t,z) is controlled by the angular velocity of solutions of two positively homogeneous and oddly symmetric systems z′=Li(t,z),i=1,2 on the left half-plane, which have rotation numbers that satisfy ρ(L1)>n/2 and ρ(L2)<(n+1)/2, and allow f(t,z) to grow superlinearly on the right half-plane. In order to estimate the rotation angle difference of solutions, we develop a system methodology of "tracking" the angle difference of solutions of the system z′=f(t,z) on each small interval on the given side under sign-varying conditions.
Citation: Chunlian Liu. Non-resonance with one-sided superlinear growth for indefinite planar systems via rotation numbers[J]. AIMS Mathematics, 2022, 7(8): 14163-14186. doi: 10.3934/math.2022781
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We consider the non-resonance with one-sided superlinear growth conditions for the indefinite planar system z′=f(t,z) from a rotation number viewpoint, and obtain the existence of 2π-periodic solutions by applying a rotation number approach together with the Poincaré-Bohl theorem. We allow that the angular velocity of solutions of z′=f(t,z) is controlled by the angular velocity of solutions of two positively homogeneous and oddly symmetric systems z′=Li(t,z),i=1,2 on the left half-plane, which have rotation numbers that satisfy ρ(L1)>n/2 and ρ(L2)<(n+1)/2, and allow f(t,z) to grow superlinearly on the right half-plane. In order to estimate the rotation angle difference of solutions, we develop a system methodology of "tracking" the angle difference of solutions of the system z′=f(t,z) on each small interval on the given side under sign-varying conditions.
The notion of lightlike submanifolds was introduced by K. L. Duggal and A. Bejancu in [1]. The study of lightlike submanifolds is remarkably more interesting due to non-trivial intersection of normal vector bundle and tangent bundle. Many geometers enriched the study of lightlike submanifolds (see [2,3]). B. Y. Chen [4] defined and studied slant submanifolds of an almost Hermitian manifold as generalization of complex submanifolds and totally real submanifolds for which the angle Ψ between ¯ϱζ and the tangent space is constant for any tangent vector field ζ. A. Lotta [5] investigated the concept of slant submanifolds in contact geometry. B. Sahin [6] studied slant submanifolds of an almost product Riemannian manifold. J. L. Cabrerizo et al. [7] analysed slant submanifolds of a Sasakian manifold. M. A. Khan et al. [8] introduced slant submanifolds in LP-contact manifolds. N. Papaghuic [9] introduced the notion of semi-slant submanifolds of Kaehler manifold. P. Alegre and A. Carriazo [10] introduced and studied bi-slant submanifolds of a para Hermitian manifold. On the other hand, Crasmareanu and Hretcanu [11,12] define golden structure ¯ϱ as a (1, 1) tensor-field satisfying ¯ϱ2=¯ϱ+I. A Riemannian manifold ¯O with a golden structure ¯ϱ is called almost golden Riemannian manifold. M. A. Qayyoom and M. Ahmad (see [13,14,15]) studied hypersurfaces, warped product skew semi-invariant submanifolds, skew semi-invariant submanifolds of a golden Riemannian manifold. They also studied submanifolds of locally metallic Riemannian manifolds [16]. B. Sahin [17] studied slant lightlike submanifolds of indefinite Hermitian manifolds. R. S. Gupta and A. Sharfuddin [18] studied slant lightlike submanifolds of indefinite Kenmotsu manifolds. J. W. Lee and D. H. Jin [19] studied slant lightlike submanifolds of an indefinite Sasakian manifold. Semi-slant submanifolds were defined and studied by V. Khan et al. [20]. Thereafter, many geometers studied semi-slant submanifolds in various spaces (see [21,22,23]). Moreover, many authors studied geometry of bi-slant lightlike submanifolds [24,25]. N. Poyraz and E. Yasar [3] studied lightlike submanifolds of golden semi-Riemannian manifolds. S. Kumar and A. Yadav [26] studied semi-slant lightlike submanifolds of golden semi-Riemannian manifolds. Johnson and Whitt studied foliations that has great importance in diffrential geometry, they considered each leaf of the foliation to be a totally geodesic submanifold of the ambient space [27].
In this paper, we introduce bi-slant lightlike submanifolds of golden semi-Riemannian manifolds. The paper is organized as follows: In Section 2, we define golden semi-Riemannian manifolds and present some basic concepts of lightlike submanifolds. In Section 3, we define and investigate some results on bi-slant lightlike submanifolds of golden semi-Riemannian manifolds and give two examples. We also discuss the integrability conditions of distributions on bi-slant lightlike submanifolds. In the last section, we obtain necessary and sufficient conditions for foliations determined by distributions on bi-slant lightlike submanifolds of golden semi-Riemannian manifolds to be geodesic.
Let (¯O,g) be a semi-Riemannian manifold. A golden structure on (¯O,g) is a non-null tensor ¯ϱ of type (1, 1) which satisfies the equation
¯ϱ2=¯ϱ+I, | (2.1) |
where I is the identity transformation. We say that the metric g is ¯ϱ-compatible if
g(¯ϱζ,η)=g(ζ,¯ϱη) | (2.2) |
for all ζ, η vector fields on ¯O. If we substitute ¯ϱζ into ζ in (2.2), then we have
g(¯ϱζ,¯ϱη)=g(¯ϱζ,η)+g(ζ,η). | (2.3) |
The semi-Riemannian metric is called ¯ϱ-compatible and (¯O,¯ϱ,g) is called a golden semi-Riemannian manifold. Also, if
¯∇ζ¯ϱη=¯ϱ¯∇ζη | (2.4) |
for all ζ,η∈Γ(TO), where ¯∇ is the Levi-Civita connection with respect to g, then (¯O,¯ϱ,g) is called a locally golden semi-Riemannian manifold.
A submanifold (Om,g) immersed in a semi-Riemannian manifold (¯Om+n,¯g) is called a lightlike submanifold if the metric g induced from ¯g is degenerate and the radical distribution Rad(TO) is of rank r, where 1≤r≤m. Let S(TO) be a screen distribution which is a semi-Riemannian complementary distribution of Rad(TO) in TO, i.e., TO=Rad(TO)⊥S(TO).
Consider a screen transversal vector bundle S(TO⊥), which is a semi-Riemannian complementary vector bundle of Rad(TO) in TO⊥. Since, for any local basis {ξi} of Rad(TO), there exists a local null frame {ϖi} of sections with values in the orthogonal complement of S(TO⊥) in [S(TO)]⊥ such that ¯g(ξi,ϖj)=δij, it follows that there exists a lightlike transversal vector bundle ltr(TO) locally spanned by {ϖi}. Let tr(TO) be complementary (but not orthogonal) vector bundle to TO in T¯O|O. Then
tr(TO)=ltr(TO)⊥S(TO⊥), |
T¯O|O=S(TO)⊥[Rad(TO)⊕ltr(TO)]⊥S(TO⊥). |
A submanifold (O,g,S(TO),S(TO⊥)) of ¯O is said to be
(i) r-lightlike if r<min{m,n};
(ii) Coisotropic if r=n<m,S(TO⊥)={0};
(iii) Isotropic if r=m<n,S(TO)={0};
(iv) Totally lightlike if r=m=n,S(TO)={0}=S(TO⊥).
Let ¯∇, ∇ and ∇t denote the linear connections on ¯O, O and vector bundle tr(TO), respectively. Then the Gauss and Weingarten formulae are given by
¯∇ζη=∇ζη+h(ζ,η),∀ζ,η∈Γ(TO), | (2.5) |
¯∇ζη=−Aηζ+∇tζη,∀ζ∈Γ(TO),η∈Γtr(TO), |
where {∇ζη,Aηζ} and {h(ζ,η),∇tζη} belong to Γ(TO) and Γ(ltr(TO)), respectively. ∇ and ∇tζ are linear connections on O and on the vector bundle ltr(TO), respectively. The second fundamental form h is a symmetric F(O)-bilinear form on Γ(TO) with values in Γ(tr(TO)) and the shape operator Aη is a linear endomorphism of Γ(TO). Then we have
¯∇ζη=∇ζη+hl(ζ,η)+hs(ζ,η), | (2.6) |
¯∇ζϖ=−Aϖζ+∇lζ(ϖ)+Ds(ζ,ϖ), | (2.7) |
¯∇ζω=−Aωζ+∇sζ(ω)+Dl(ζ,ω),∀ζ,η∈Γ(TO),ϖ∈Γ(ltr(TO)) | (2.8) |
and ω∈Γ(S(TO⊥)). Denote the projection of TO on S(TO) by ¯P. Then, by using (2.1), (2.3)–(2.5) and having the fact that ¯∇ is a metric connection we obtain
¯g(hs(ζ,η),ω)+¯g(η,Dl(ζ,ω))=g(Aωζ,η), |
¯g(Ds(ζ,ϖ),ω)=¯g(ϖ,Aωζ). |
We set
∇ζ¯Pη=∇∗ζ¯Pη+h∗(ζ,¯Pη), | (2.9) |
∇ζξ=−A∗ξζ+∇∗tζξ | (2.10) |
for ζ,η∈Γ(TO) and ξ∈Γ(RadTO). By using above equations, we obtain
¯g(hl(ζ,¯Pη),ξ)=g(A∗ξζ,¯Pη), |
¯g(h∗(ζ,¯Pη),ϖ)=g(Aϖζ,¯Pη), |
¯g(hl(ζ,ξ),ξ)=0,A∗ξξ=0. |
In general, the induced connection ∇ on O is not metric connection. Since ¯∇ is a metric connection, by using (2.3) we get
(∇ζg)(η,ς)=¯g(hl(ζ,η),ς)+¯g(hl(ζ,ς),η). |
However, it is important to note that ∇∗ is a metric connection on S(TO). From now on, we briefly denote (O,g,S(TO),S(TO⊥)) by O in this paper.
To define bi-slant lightlike submanifolds, we require a lemma:
Lemma 3.1. [28] Let O be a q-lightlike submanifold of a golden semi-Riemannian manifold ¯O of index 2q. Suppose there exists a screen distribution S(TO) such that ¯ϱRad(TO)⊂S(TO) and ¯ϱltr(TO)⊂S(TO). Then, ¯ϱRad(TO)⋂¯ϱltr(TO)={0} and any complementary distribution to ¯ϱRad(TO)⊕¯ϱltr(TO) in S(TO) is Riemannian.
Definition 3.1. Let O be a q-lightlike submanifold of a golden semi-Riemannian manifold ¯O of index 2q such that 2q<dim(O). Then, we say that O is a bi-slant lightlike submanifold of ¯O if the following conditions are satisfied:
(i) ¯ϱRad(TO) is a distribution on O such that Rad(TO)⋂¯ϱRadTO={0};
(ii) there exists non-degenerate orthogonal distributions D, D1 and D2 on O such that
S(TO)=(¯ϱRad(TO)⊕¯ϱltr(TO))⊥D⊥D1⊥D2; |
(iii) the distribution D is an invariant distribution, i.e., ¯ϱD=D;
(iv) the distribution D1 is slant with angle Ψ1(≠0), i.e., for each ζ∈O and each non-zero vector ζ∈(D1)ζ, the angle Ψ1 between ¯ϱζ and the vector space (D1)ζ is a non-zero constant, which is independent of the choice of ζ∈O and ζ∈(D1)ζ;
(v) the distribution D2 is slant with angle Ψ2(≠0), i.e., for each ζ∈O and each non-zero vector ζ∈(D2)ζ, the angle Ψ2 between ¯ϱζ and the vector space (D2)ζ is a non-zero constant, which is independent of the choice of ζ∈O and ζ∈(D2)ζ.
These constant angle Ψ1 and Ψ2 are called the slant angles of distributions D1 and D2 respectively. A bi-slant lightlike submanifold is said to be proper if D1≠{0},D2≠{0} and Ψ1≠π2, Ψ2≠π2.
From the above definition, we have the following decomposition
TO=Rad(TO)⊥(¯ϱRad(TO)⊕¯ϱltr(TO))⊥D⊥D1⊥D2. |
In particular, we have
(i) If D=0, and any one of D1 and D2 is zero, then O is a slant lightlike submanifold;
(ii) If D≠0, and any one of D1 and D2 is zero, then O is a semi-slant lightlike submanifold;
(iii) If D≠0 and Ψ1=π2,Ψ2=π2, then O is CR-lightlike submanifold.
Thus, the above new class of lightlike submanifolds of a golden semi-Riemannian manifold includes slant, semi-slant and Cauchy-Riemann lightlike submanifolds as its subcases.
Example 3.1. Let (R162,¯g) be a semi-Euclidean space of signature (−,−,+,+,+,+,+,+,+,+,+,+,+,+,+,+) with respect to the canonical basis {∂ζ1,∂ζ2,∂ζ3,∂ζ4,∂ζ5,∂ζ6,∂ζ7,∂ζ8,∂ζ9,∂ζ10,∂ζ11,∂ζ12,∂ζ13,∂ζ14,∂ζ15,∂ζ16} with the golden structure ¯ϱ defined by
¯ϱ(ζ1,ζ2,ζ3,ζ4,ζ5,ζ6,ζ7,ζ8,ζ9,ζ10,ζ11,ζ12,ζ13,ζ14,ζ15,ζ16)=(τζ1,¯τζ2,τζ3,¯τζ4,¯τζ5,¯τζ6,¯τζ7,¯τζ8,¯τζ9,¯τζ10,τζ11,τζ12,τζ13,τζ14,τζ15,τζ16), |
where τ=1+√52 and ¯τ=1−√52 are the roots of ζ2−ζ−1=0. Thus, ¯ϱ2=¯ϱ+I and ¯ϱ is a golden structure on R162.
Let O be a 9-dimensional submanifold of (R162,¯g) given by
ζ1=η1+τη2−τη3,ζ2=τη1−η2+η3,ζ3=η1+τη2+τη3,ζ4=−τη1+η2+η3,ζ5=¯τη4,ζ6=¯τη5,ζ7=τη4,ζ8=τη5,ζ9=¯τη6,ζ10=¯τη7,ζ11=τη6,ζ12=τη7,ζ13=¯τη8,ζ14=¯τη9,ζ15=τη8,ζ16=τη9. |
Then, TO is spanned by ς1,ς2,ς3,ς4,ς5,ς6,ς7,ς8,ς9, where
ς1=∂ζ1+τ∂ζ2+∂ζ3−τ∂ζ4,ς2=τ∂ζ1−∂ζ2+τ∂ζ3+∂ζ4,ς3=−τ∂ζ1+∂ζ2+τ∂ζ3+∂ζ4,ς4=¯τ∂ζ5+τ∂ζ7,ς5=¯τ∂ζ6+τ∂ζ8,ς6=¯τ∂ζ9+τ∂ζ11,ς7=¯τ∂ζ10+τ∂ζ12,ς8=¯τ∂ζ13+τ∂ζ15,ς9=¯τ∂ζ14+τ∂ζ16. |
This implies that Rad(TO)=span{ς1} and S(TO)=span{ς2,ς3,ς4,ς5,ς6,ς7,ς8,ς9}.
Now, ltr(TO) is spannned by
ϖ=12(2+τ){−∂ζ1−τ∂ζ2+∂ζ3−τ∂ζ4} |
and S(TO⊥) is spanned by
ω1=τ∂ζ5−¯τ∂ζ7,ω2=τ∂ζ6−¯τ∂ζ8,ω3=τ∂ζ9−¯τ∂ζ11,ω4=τ∂ζ10−¯τ∂ζ12,ω5=τ∂ζ13−¯τ∂ζ15,ω6=τ∂ζ14−¯τ∂ζ16. |
Now, ¯ϱς1=ς2,¯ϱϖ=ς3 and ¯ϱς4=¯τς4,¯ϱς5=¯τς5, which means D is invariant, i.e., ¯ϱD=D and D=span{ς4,ς5} and D1=span{ς6,ς7},D2=span{ς8,ς9} are slant distributions with slant angles Ψ1=arccos(4√21) and Ψ2=arccos(1+√5√2(3+√5)) respectively. Hence, O is a bi-slant 1-lightlike submanifold of R162.
Example 3.2. Let (R164,¯g) be a semi-Euclidean space of signature (+,+,−,−,+,+,+,+,+,+,+,−,+,+,+,−) with respect to the canonical basis {∂ζ1,∂ζ2,∂ζ3,∂ζ4,∂ζ5,∂ζ6,∂ζ7,∂ζ8,∂ζ9,∂ζ10,∂ζ11,∂ζ12,∂ζ13,∂ζ14,∂ζ15,∂ζ16} with the golden structure ¯ϱ defined by
¯ϱ(ζ1,ζ2,ζ3,ζ4,ζ5,ζ6,ζ7,ζ8,ζ9,ζ10,ζ11,ζ12,ζ13,ζ14,ζ15,ζ16)=(¯τζ1,τζ2,¯τζ3,τζ4,τζ5,τζ6,¯τζ7,¯τζ8,¯τζ9,τζ10,¯τζ11,¯τζ12,¯τζ13,τζ14,¯τζ15,¯τζ16), |
where τ=1+√52 and ¯τ=1−√52 are the roots of ζ2−ζ−1=0. Thus, ¯ϱ2=¯ϱ+I and ¯ϱ is a golden structure on R164.
Let O be a 9-dimensional submanifold of (R164,¯g) given by
ζ1=τη1−η2−η3,ζ2=η1+τη2+τη3,ζ3=τη1−η2+η3,ζ4=η1+τη2−τη3,ζ5=τη4,ζ6=¯τη4,ζ7=τη5,ζ8=¯τη5,ζ9=τη6,ζ10=¯τη6,ζ11=τη7,ζ12=¯τη7,ζ13=τη8,ζ14=¯τη8,ζ15=τη9,ζ16=¯τη9. |
Then, TO is spanned by ς1,ς2,ς3,ς4,ς5,ς6,ς7,ς8,ς9, where
ς1=τ∂ζ1+∂ζ2+τ∂ζ3+∂ζ4,ς2=−∂ζ1+τ∂ζ2−∂ζ3+τ∂ζ4,ς3=−∂ζ1+τ∂ζ2+∂ζ3−τ∂ζ4,ς4=τ∂ζ5+¯τ∂ζ6,ς5=τ∂ζ7+¯τ∂ζ8,ς6=τ∂ζ9+¯τ∂ζ10,ς7=τ∂ζ11+¯τ∂ζ12,ς8=τ∂ζ13+¯τ∂ζ14,ς9=τ∂ζ15+¯τ∂ζ16. |
This implies that Rad(TO)=span{ς1} and S(TO)=span{ς2,ς3,ς4,ς5,ς6,ς7,ς8,ς9}.
Now, ltr(TO) is spannned by
ϖ=12(2+τ){τ∂ζ1+∂ζ2−τ∂ζ3−∂ζ4}, |
and S(TO⊥) is spanned by
ω1=¯τ∂ζ5−τ∂ζ6,ω2=¯τ∂ζ7−τ∂ζ8,ω3=¯τ∂ζ9−τ∂ζ10,ω4=¯τ∂ζ11+τ∂ζ12,ω5=¯τ∂ζ13−τ∂ζ14,ω6=¯τ∂ζ15+τ∂ζ16. |
Now, ¯ϱς1=ς2,¯ϱϖ=ς3 and ¯ϱς4=τς4,¯ϱς5=¯τς5, which means D is invariant, i.e., ¯ϱD=D and D=span{ς4,ς5} and D1=span{ς6,ς8},D2=span{ς7,ς9} are slant distributions with slant angles Ψ1=arccos(−1√6) and Ψ2=arccos(1−√5√2(3−√5)) respectively. Hence, O is a bi-slant 1-lightlike submanifold of R164.
Further, for any vector field ζ tangent to O, we put
¯ϱζ=fζ+Fζ, | (3.1) |
where fζ and Fζ are tangential and transversal parts of ¯ϱζ respectively. We denote the projections on Rad(TO),¯ϱRad(TO),¯ϱltr(TO),D,D1 and D2 in TO by P1,P2,P3,P4,P5 and P6 respectively. Similarly, we denote the projections of tr(TO) on ltr(TO) and S(TO⊥) by Q1 and Q2 respectively. Thus, for any ζ∈Γ(TO), we get
ζ=P1ζ+P2ζ+P3ζ+P4ζ+P5ζ+P6ζ. |
Now, applying ¯ϱ to above, we get
¯ϱζ=¯ϱP1ζ+¯ϱP2ζ+¯ϱP3ζ+¯ϱP4ζ+¯ϱP5ζ+¯ϱP6ζ, |
which gives
¯ϱζ=¯ϱP1ζ+¯ϱP2ζ+¯ϱP3ζ+¯ϱP4ζ+fP5ζ+FP5ζ+fP6ζ+FP6ζ, | (3.2) |
where ¯ϱP2ζ=K1¯ϱP2ζ+K2¯ϱP2ζ,¯ϱP3ζ=L1¯ϱP3ζ+L2¯ϱP3ζ and fP5ζ,fP6ζ (resp. FP5ζ,FP6ζ) denotes the tangential (resp. transversal) component of ¯ϱP5ζ and ¯ϱP6ζ. Thus, we get ¯ϱP1ζ∈Γ(¯ϱRad(TO)),K1¯ϱP2ζ∈Γ(RadTO),K2¯ϱP2ζ∈Γ(¯ϱRad(TO)),L1¯ϱP3ζ∈Γ(ltr(TO)),L2¯ϱP3ζ∈Γ(¯ϱltr(TO)),¯ϱP4ζ∈Γ(¯ϱD),fP5ζ∈Γ(D1),fP6ζ∈Γ(D2) and FP5ζ,FP6ζ∈Γ(S(TO⊥)). Also, for any ω∈Γ(tr(TO)), we have
ω=Q1ω+Q2ω. |
Applying ¯ϱ to above, we obtain
¯ϱω=¯ϱQ1ω+¯ϱQ2ω, |
which gives
¯ϱω=¯ϱQ1ω+BQ′2ω+CQ′2ω+BQ″2ω+CQ″2ω, | (3.3) |
where BQ′2ω,BQ″2ω(resp. CQ′2ω,CQ″2ω) denote the tangential(resp. transversal) component of ¯ϱQ2ω. Thus, we get ¯ϱQ1ω∈Γ(¯ϱltr(TO)),BQ′2ω∈Γ(D1),BQ″2ω∈Γ(D2) and CQ′2ω,CQ″2ω∈Γ(S(TO⊥)).
Theorem 3.2. Let O be a q-lightlike submanifold of a golden semi-Riemannian manifold ¯O of index 2q. Then, O is a bi-slant lightlike submanifold iff
(i) there exist a distribution ¯ϱRad(TO) on O such that Rad(TO)⋂¯ϱRad(TO)={0};
(ii) there exist a screen distribution S(TO) which can be splitted as
S(TO)=(¯ϱRad(TO)⊕¯ϱltr(TO))⊥D⊥D1⊥D2 |
such that D is an invariant distribution on O, i.e., ¯ϱD=D;
(iii) there exist a constant κ1∈[0,1) such that f2ζ=κ1(¯ϱ+I)ζ, ∀ζ∈Γ(D1);
(iv) there exist a constant κ2∈[0,1) such that f2ζ=κ2(¯ϱ+I)ζ, ∀ζ∈Γ(D2).
In that case, κ1=cos2Ψ1 and κ2=cos2Ψ2, where Ψ1 and Ψ2 represents the slant angles of D1 and D2 respectively.
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the distribution D is invariant with respect to ¯ϱ and ¯ϱRad(TO) is a distribution on O such that Rad(TO)⋂¯ϱRad(TO)={0}.
For any ζ∈Γ(D1), we have
|fζ|=|¯ϱζ|cosΨ1, |
cosΨ1=|fζ||¯ϱζ|. | (3.4) |
cos2Ψ1=|fζ|2|¯ϱζ|2=g(fζ,fζ)g(¯ϱζ,¯ϱζ)=g(ζ,f2ζ)g(ζ,¯ϱ2ζ), |
g(ζ,f2ζ)=cos2Ψ1g(ζ,¯ϱ2ζ). | (3.5) |
Since, O is a bi-slant lightlike submanifold, cos2Ψ1=κ1 (constant)∈[0,1) and therefore from (3.5), we have
g(ζ,f2ζ)=κ1g(ζ,¯ϱ2ζ)=g(ζ,κ1¯ϱ2ζ). |
For all ζ∈Γ(D1),
g(ζ,(f2−κ1¯ϱ2)ζ)=0. | (3.6) |
Since, (f2−κ1¯ϱ2)ζ∈Γ(D1) and the induced metric g=g|D1×D1 is non-degenerate (positive definite), from (3.6), we have
(f2−κ1¯ϱ2)ζ=0, |
f2ζ=κ1¯ϱ2ζ=κ1(¯ϱ+I)ζ,∀ζ∈Γ(D1). | (3.7) |
This proves (iii).
Suppose for any ζ∈Γ(D2), we have
|fζ|=|¯ϱζ|cosΨ2, |
cosΨ2=|fζ||¯ϱζ|. | (3.8) |
Now, by using similar steps as in proof of (iii), we obtain
f2ζ=κ2(¯ϱ+I)ζ,∀ζ∈Γ(D2), | (3.9) |
which proves (iv).
Conversely, suppose that conditions (i)–(iv) are satisfied. From (iii), we have f2ζ=κ1¯ϱ2ζ for all ζ∈Γ(D1), where κ1(constant)∈[0,1).
Now,
cosΨ1=g(¯ϱζ,fζ)|¯ϱζ||fζ|=g(ζ,¯ϱfζ)|¯ϱζ||fζ|=g(ζ,f(fζ)+F(fζ))|¯ϱζ||fζ|. |
Using (3.7), we have
cosΨ=g(ζ,f2ζ)|¯ϱζ||fζ|=g(ζ,κ1¯ϱ2ζ)|¯ϱζ||fζ|=κ1g(ζ,¯ϱ2ζ)|¯ϱζ||fζ|=κ1g(ζ,¯ϱ(¯ϱζ))|¯ϱζ||fζ|, |
cosΨ1=κ1g(¯ϱζ,¯ϱζ)|¯ϱζ||fζ|=κ1|¯ϱζ|2|¯ϱζ||fζ|, |
cosΨ1=κ1|¯ϱζ||fζ|. |
Using (3.4), we have
cosΨ1=κ11cosΨ1, |
cos2Ψ1=κ1(constant). |
Further, from (iv) we have f2ζ=κ2¯ϱ2ζ for all ζ∈Γ(D2), where κ2(constant)∈[0,1). Now, by proceeding in the same way as above, we get cos2Ψ2=κ2(constant). This completes the proof. Hence, O is a bi-slant lightlike submanifold.
Theorem 3.3. Let O be a q-lightlike submanifold of a golden semi-Riemannian manifold ¯O of index 2q. Then, O is a bi-slant lightlike submanifold iff
(i) there exist a distribution ¯ϱRad(TO) on O such that Rad(TO)⋂¯ϱRad(TO)={0};
S(TO)=(¯ϱRad(TO)⊕¯ϱltr(TO))⊥D⊥D1⊥D2 |
such that D is an invariant distribution on O, i.e., ¯ϱD=D;
(ii) there exist a constant ν1∈[0,1) such that BFζ=ν1(¯ϱ+I)ζ, ∀ζ∈Γ(D1);
(iii) there exist a constant ν2∈[0,1) such that BFζ=ν2(¯ϱ+I)ζ, ∀ζ∈Γ(D2).
In that case, ν1=sin2Ψ1 and ν2=sin2Ψ2, where Ψ1 and Ψ2 represents the slant angles of D1 and D2, respectively.
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the distribution D is invariant with respect to ¯ϱ and ¯ϱRad(TO) is a distribution on O such that Rad(TO)⋂¯ϱRad(TO)={0}.
Now, ∀ vector field ζ∈Γ(D1), we have
¯ϱζ=fζ+Fζ, | (3.10) |
where fζ and Fζ represents the tangential and transversal parts of ¯ϱζ respectively. Applying ¯ϱ to (3.10), we get
¯ϱ2ζ=¯ϱfζ+¯ϱFζ, |
¯ϱ2ζ=f(fζ)+F(fζ)+B(Fζ)+C(Fζ). |
Now, comparing the tangential components, we get
¯ϱ2ζ=f2ζ+BFζ,∀ζ∈Γ(D2). | (3.11) |
Since, O is a bi-slant lightlike submanifold, f2ζ=κ1¯ϱ2ζ,∀ζ∈Γ(D1), where κ1(constant)∈[0,1). From (3.11), we get
¯ϱ2ζ=κ1¯ϱ2ζ+BFζ, |
(1−κ1)¯ϱ2ζ=BFζ, |
BFζ=ν1¯ϱ2ζ=ν1(¯ϱ+I)ζ,∀ζ∈Γ(D1), | (3.12) |
where 1−κ1=ν1(constant)∈[0,1).
This proves (iii).
Suppose for any ζ∈Γ(D2), we have
¯ϱζ=fζ+Fζ, | (3.13) |
where fζ and Fζ are the tangential and transversal parts of ¯ϱζ respectively.
Now, by using similar steps as in proof of (iii), we obtain
BFζ=ν2¯ϱ2ζ=ν2(¯ϱ+I)ζ,∀ζ∈Γ(D2), | (3.14) |
where 1−κ2=ν2(constant)∈[0,1).
This proves (iv).
Conversely, suppose that conditions (i)–(iv) are satisfied. From (3.11), we have
¯ϱ2ζ=f2ζ+ν1¯ϱ2ζ,∀ζ∈Γ(D1), |
f2ζ=(1−ν1)¯ϱ2ζ, |
f2ζ=κ1¯ϱ2ζ=κ1(¯ϱ+I)ζ,∀ζ∈Γ(D1), | (3.15) |
where 1−ν1=κ1(constant)∈[0,1).
Furthermore, from (iv) we have BFζ=ν2¯ϱ2ζ, for all ζ∈Γ(D2), where ν2(constant)∈[0,1). Now, by proceeding in the same way as above, we get
f2ζ=κ2¯ϱ2ζ=κ2(¯ϱ+I)ζ,∀ζ∈Γ(D2), | (3.16) |
where 1−ν2=κ2(constant)∈[0,1). Now, the proof follows from Theorem 3.2.
Hence, O is a bi-slant lightlike submanifold.
Corollary 3.1. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then for any slant distribution D′ of O with slant angle Ψ, we have
g(fζ,fη)=cos2Ψ[g(¯ϱζ,η)+g(ζ,η)], |
g(Fζ,Fη)=sin2Ψ[g(¯ϱζ,η)+g(ζ,η)], |
∀ζ,η∈Γ(D′).
The proof of the above corollary follows by using similar steps as in the proof of Corollary 3.1 of [17].
Theorem 3.4. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the integrability of Rad(TO) holds iff
(i) ¯g(hl(ζ,¯ϱη),ξ)=¯g(hl(η,¯ϱζ),ξ);
(ii) ¯g(h∗(ζ,¯ϱη),ϖ)=¯g(h∗(η,¯ϱζ),ϖ);
(iii) ¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,¯Jς)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς);
(iv) ¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς1)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς1)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς1);
(v) ¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς2)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς2)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς2)
∀ζ,η,ξ∈Γ(RadTO),ς∈Γ(D),ς1∈Γ(D1),ς2∈Γ(D2) and ϖ∈Γ(ltr(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Rad(TO) is integrable iff
¯g([ζ,η],¯ϱξ)=¯g([ζ,η],¯ϱϖ)=¯g([ζ,η],ς)=¯g([ζ,η],ς1)=¯g([ζ,η],ς2)=0, |
∀ζ,η,ξ∈Γ(RadTO),ς∈Γ(D),ς1∈Γ(D1),ς2∈Γ(D2) and ϖ∈Γ(ltr(TO)).¯∇ being a metric connection and using (2.3),(2.6),(2.9) and (3.1), we obtain
¯g([ζ,η],¯ϱξ)=¯g(¯∇ζη−¯∇ηζ,¯ϱξ)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),ξ)=¯g(¯ϱ¯∇ζη−¯ϱ¯∇ηζ),ξ)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ξ)=¯g(hl(ζ,¯ϱη)−hl(η,¯ϱζ),ξ), | (3.17) |
¯g([ζ,η],¯ϱϖ)=¯g(¯∇ζη−¯∇ηζ,¯ϱϖ)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),ϖ)=¯g(¯ϱ¯∇ζη−¯ϱ¯∇ηζ),ϖ)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ϖ)=¯g(h∗(ζ,¯ϱη)−h∗(η,¯ϱζ),ϖ), | (3.18) |
¯g([ζ,η],ς)=¯g(¯ϱ[ζ,η],¯ϱς)−¯g(¯ϱ[ζ,η],ς)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),¯ϱς)−¯g(¯ϱ(¯∇ζη−¯∇ηζ),ς)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,¯ϱς)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ς)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,¯ϱς)−¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς), | (3.19) |
¯g([ζ,η],ς1)=¯g(¯ϱ[ζ,η],¯ϱς1)−¯g(¯ϱ[ζ,η],ς1)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,fς1+Fς1)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ς1)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς1)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς1)−¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς1). | (3.20) |
¯g([ζ,η],ς2)=¯g(¯ϱ[ζ,η],¯ϱς2)−¯g(¯ϱ[ζ,η],ς2)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,fς2+Fς2)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ς2)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς2)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς2)−¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς2). | (3.21) |
Now, the proof follows from (3.17)–(3.21).
Theorem 3.5. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the integrability of ¯ϱRad(TO) holds iff
(i) ¯g(hl(¯ϱζ,η)−hl(¯ϱη,ζ),¯ϱξ)=−¯g(hl(¯ϱζ,η)−hl(¯ϱη,ζ),ξ);
(ii) ¯g(A∗ζ¯ϱη,¯ϱς)=¯g(A∗η¯ϱζ,¯ϱς);
(iii) ¯g(A∗ζ¯ϱη−A∗η¯ϱζ,fς1)=¯g(hs(¯ϱη,ζ)−hs(¯ϱζ,η),Fς1);
(iv) ¯g(A∗ζ¯ϱη−A∗η¯ϱζ,fς2)=¯g(hs(¯ϱη,ζ)−hs(¯ϱζ,η),Fς2);
(v) ¯g(Aϖ¯ϱζ,¯ϱη)=¯g(Aϖ¯ϱη,¯ϱζ)
∀ζ,η,ξ∈Γ(RadTO),ς∈Γ(D),ς1∈Γ(D1),ς2∈Γ(D2) and ϖ∈Γ(ltr(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. ¯ϱRad(TO) is integrable iff
¯g([¯ϱζ,¯ϱη],¯ϱξ)=¯g([¯ϱζ,¯ϱη],ς)=¯g([¯ϱζ,¯ϱη],ς1)=¯g([¯ϱζ,¯ϱη],ς2)=¯g([¯ϱζ,¯ϱη],ϖ)=0, |
∀ζ,η,ξ∈ΓRad(TO),ς∈Γ(D),ς1∈Γ(D1),ς2∈Γ(D2) and ϖ∈Γ(ltr(TO)).¯∇ being a metric connection and using (2.3),(2.6),(2.7),(2.10) and (3.1), we obtain
¯g([¯ϱζ,¯ϱη],¯ϱξ)=¯g(¯∇¯ϱζ¯ϱη−¯∇¯ϱη¯ϱζ,¯ϱξ)=¯g(¯ϱ¯∇¯ϱζη−¯ϱ¯∇¯ϱηζ,¯ϱξ)=¯g(¯ϱ(¯∇¯ϱζη−¯∇¯ϱηζ),¯ϱξ)=¯g(¯ϱ(¯∇¯ϱζη−¯∇¯ϱηζ),ξ)+¯g(¯∇¯ϱζη−¯∇¯ϱηζ,ξ)=¯g(¯∇¯ϱζη−¯∇¯ϱηζ,¯ϱξ)+¯g(hl(¯ϱζ,η)−hl(¯ϱη,ζ),ξ)=¯g(hl(¯ϱζ,η)−hl(¯ϱη,ζ),¯ϱξ)+¯g(hl(¯ϱζ,η)−hl(¯ϱη,ζ),ξ), | (3.22) |
¯g([¯ϱζ,¯ϱη],ς)=¯g(¯∇¯ϱζ¯ϱη−¯∇¯ϱη¯ϱζ,ς)=¯g(¯ϱ¯∇¯ϱζη−¯ϱ¯∇¯ϱηζ,ς)=¯g(¯ϱ(¯∇¯ϱζη−¯∇¯ϱηζ),ς)=¯g(¯∇¯ϱζη−¯∇¯ϱηζ,¯ϱς)=¯g(¯∇¯ϱζη,¯ϱς)−¯g(¯∇¯ϱηζ,¯ϱς)=−¯g(A∗η¯ϱζ,¯ϱς)+¯g(A∗ζ¯ϱη,¯ϱς)=¯g(A∗ζ¯ϱη,¯ϱς)−¯g(A∗η¯ϱζ,¯ϱς), | (3.23) |
¯g([¯ϱζ,¯ϱη],ς1)=¯g(¯∇¯ϱζ¯ϱη−¯∇¯ϱη¯ϱζ,ς1)=¯g(¯ϱ¯∇¯ϱζη−¯ϱ¯∇¯ϱηζ,ς1)=¯g(¯ϱ(¯∇¯ϱζη−¯∇¯ϱηζ),ς1)=¯g(¯∇¯ϱζη−¯∇¯ϱηζ,¯ϱς1)=¯g(¯∇¯ϱζη−¯∇¯ϱηζ,fς1+Fς1)=¯g(¯∇¯ϱζη,fς1+Fς1)−¯g(¯∇¯ϱηζ,fς1+Fς1)=−¯g(A∗η¯ϱζ,fς1)+¯g(hs(¯ϱζ,η),Fς1)+¯g(A∗ζ¯ϱη,fς1)−¯g(hs(¯ϱη,ζ),Fς1)=¯g(A∗ζ¯ϱη−A∗η¯ϱζ,fς1)−¯g(hs(¯ϱη,ζ)−hs(¯ϱζ,η),Fς1), | (3.24) |
¯g([¯ϱζ,¯ϱη],ς2)=¯g(¯∇¯ϱζ¯ϱη−¯∇¯ϱη¯ϱζ,ς2)=¯g(¯ϱ¯∇¯ϱζη−¯ϱ¯∇¯ϱηζ,ς2)=¯g(¯ϱ(¯∇¯ϱζη−¯∇¯ϱηζ),ς2)=¯g(¯∇¯ϱζη−¯∇¯ϱηζ,¯ϱς2)=¯g(¯∇¯ϱζη−¯∇¯ϱηζ,fς2+Fς2)=¯g(¯∇¯ϱζη,fς2+Fς2)−¯g(¯∇¯ϱηζ,fς2+Fς2)=−¯g(A∗η¯ϱζ,fς2)+¯g(hs(¯ϱζ,η),Fς2)+¯g(A∗ζ¯ϱη,fς2)−¯g(hs(¯ϱη,ζ),Fς2)=¯g(A∗ζ¯ϱη−A∗η¯ϱζ,fς2)−¯g(hs(¯ϱη,ζ)−hs(¯ϱζ,η),Fς2), | (3.25) |
¯g([¯ϱζ,¯ϱη],ϖ)=¯g(¯∇¯ϱζ¯ϱη−¯∇¯ϱη¯ϱζ,ϖ)=¯g(¯∇¯ϱζ¯ϱη,ϖ)−¯g(¯∇¯ϱη¯ϱζ,ϖ)=−¯g(¯ϱη,¯∇¯ϱζϖ)+¯g(¯ϱζ,¯∇¯ϱηϖ)=−¯g(¯∇¯ϱζϖ,¯ϱη)+¯g(¯∇¯ϱηϖ,¯ϱζ)=¯g(Aϖ¯ϱζ,¯ϱη)−¯g(Aϖ¯ϱη,¯ϱζ). | (3.26) |
Now, the proof follows from (3.22)–(3.26).
Theorem 3.6. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the integrability of ¯ϱltr(TO) holds iff
(i) ¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,¯ϱϖ)=−¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,ϖ);
(ii) ¯g(Aϖ1¯ϱϖ2,¯ϱς)=¯g(Aϖ2¯ϱϖ1,¯ϱς);
(iii) ¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,fς1)=¯g(Ds(¯ϱϖ2,ϖ1)−Ds(¯ϱϖ1,ϖ2),Fς1);
(iv)¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,fς2)=¯g(Ds(¯ϱϖ2,ϖ1)−Ds(¯ϱϖ1,ϖ2),Fς2);
(v) ¯g(Aϖ¯ϱϖ1,¯ϱϖ2)=¯g(Aϖ¯ϱϖ2,¯ϱϖ1)
∀ϖ1,ϖ2,ϖ∈Γ(ltr(TO)),ς∈Γ(D),ς1∈Γ(D1) and ς2∈Γ(D2).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. ¯ϱltr(TO) is integrable iff
¯g([¯ϱϖ1,¯ϱϖ2],¯ϱϖ)=¯g([¯ϱϖ1,¯ϱϖ2],ς)=¯g([¯ϱϖ1,¯ϱϖ2],ς1)=¯g([¯ϱϖ1,¯ϱϖ2],ς2)=¯g([¯ϱϖ1,¯ϱϖ2],ϖ)=0, |
∀ϖ1,ϖ2,ϖ∈Γ(ltr(TO)),ς∈Γ(D),ς1∈Γ(D1) and ς2∈Γ(D2).¯∇ being a metric connection and using (2.3),(2.6),(2.7),(2.9) and (3.1), we obtain
¯g([¯ϱϖ1,¯ϱϖ2],¯ϱϖ)=¯g(¯∇¯ϱϖ1¯ϱϖ2−¯∇¯ϱϖ2¯ϱϖ1,¯ϱϖ)=¯g(¯ϱ¯∇¯ϱϖ1ϖ2−¯ϱ¯∇¯ϱϖ2ϖ1,¯ϱϖ)=¯g(¯ϱ(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1),¯ϱϖ)=¯g(¯ϱ(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1),ϖ)+¯g(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1,ϖ)=¯g(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1,¯ϱϖ)+¯g(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1,ϖ)=¯g(−Aϖ2¯ϱϖ1+Aϖ1¯ϱϖ2,¯ϱϖ)+¯g(−Aϖ2¯ϱϖ1+Aϖ1¯ϱϖ2,ϖ)=¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,¯ϱϖ)+¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,ϖ), | (3.27) |
¯g([¯ϱϖ1,¯ϱϖ2],ς)=¯g(¯∇¯ϱϖ1¯ϱϖ2−¯∇¯ϱϖ2¯ϱϖ1,ς)=¯g(¯ϱ¯∇¯ϱϖ1ϖ2−¯ϱ¯∇¯ϱϖ2ϖ1,ς)=¯g(¯ϱ(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1),ς)=¯g(¯∇¯ϱϖ1ϖ2−¯∇¯ϱϖ2ϖ1,¯ϱς)=¯g(¯∇¯ϱϖ1ϖ2,¯ϱς)−¯g(¯∇¯ϱϖ2ϖ1,¯ϱς)=−¯g(Aϖ2¯ϱϖ1,¯ϱς)+¯g(Aϖ1¯ϱϖ2,¯ϱς)=¯g(Aϖ1¯ϱϖ2,¯ϱς)−¯g(Aϖ2¯ϱϖ1,¯ϱς), | (3.28) |
¯g([¯ϱϖ1,¯ϱϖ2],ς1)=¯g(¯∇¯ϱϖ1¯ϱϖ2−¯∇¯ϱϖ2¯ϱϖ1,ς1)=¯g(¯ϱ¯∇¯ϱϖ1ϖ2−¯ϱ¯∇¯ϱϖ2ϖ1,ς1)=−¯g(Aϖ2¯ϱϖ1,fς1)+¯g(Aϖ1¯ϱϖ2,fς1)+¯g(Ds(¯ϱϖ1,ϖ2),Fς1)−¯g(Ds(¯ϱϖ2,ϖ1),Fς1)=¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,fς1)−¯g(Ds(¯ϱϖ2,ϖ1)−Ds(¯ϱϖ1,ϖ2),Fς1), | (3.29) |
¯g([¯ϱϖ1,¯ϱϖ2],ς2)=¯g(¯∇¯ϱϖ1¯ϱϖ2−¯∇¯ϱϖ2¯ϱϖ1,ς2)=¯g(¯ϱ¯∇¯ϱϖ1ϖ2−¯ϱ¯∇¯ϱϖ2ϖ1,ς2)=−¯g(Aϖ2¯ϱϖ1,fς2)+¯g(Aϖ1¯ϱϖ2,fς2)+¯g(Ds(¯ϱϖ1,ϖ2),Fς2)−¯g(Ds(¯ϱϖ2,ϖ1),Fς2)=¯g(Aϖ1¯ϱϖ2−Aϖ2¯ϱϖ1,fς2)−¯g(Ds(¯ϱϖ2,ϖ1)−Ds(¯ϱϖ1,ϖ2),Fς2), | (3.30) |
¯g([¯ϱϖ1,¯ϱϖ2],ϖ)=¯g(¯∇¯ϱϖ1¯ϱϖ2−¯∇¯ϱϖ2¯ϱϖ1,ϖ)=¯g(¯∇¯ϱϖ1¯ϱϖ2,ϖ)−¯g(¯∇¯ϱϖ2¯ϱϖ1,ϖ)=−¯g(¯ϱϖ2,¯∇¯ϱϖ1ϖ)+¯g(¯ϱϖ1,¯∇¯ϱϖ2ϖ)=−¯g(¯∇¯ϱϖ1ϖ,¯ϱϖ2)+¯g(¯∇¯ϱϖ2ϖ,¯ϱϖ1)=¯g(Aϖ¯ϱϖ1,¯ϱϖ2)−¯g(Aϖ¯ϱϖ2,¯ϱϖ1). | (3.31) |
The proof follows from (3.27)–(3.31).
Theorem 3.7. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the integrability of D holds iff
(i) ¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς1)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς1)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς1);
(ii) ¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς2)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς2)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς2);
(iii) ¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,¯ϱϖ)=¯g(h∗(ζ,¯ϱη)−h∗(η,¯ϱζ),ϖ);
(iii) ¯g(Aϖζ,¯ϱη)=¯g(Aϖη,¯ϱζ); ∀ζ,η∈Γ(D),ς1∈Γ(D1),ς2∈Γ(D2) and ϖ∈Γ(ltr(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. D is integrable iff
¯g([ζ,η],ς1)=¯g([ζ,η],ς2)=¯g([ζ,η],ϖ)=¯g([ζ,η],¯ϱϖ)=0, |
∀ζ,η∈Γ(D),ς1∈Γ(D1),ς2∈Γ(D2) and ϖ∈Γ(ltr(TO)). ¯∇ being a metric connection and using (2.3),(2.6),(2.7),(2.9) and (3.1), we obtain
¯g([ζ,η],ς1)=¯g(¯ϱ[ζ,η],¯ϱς1)−¯g(¯ϱ[ζ,η],ς1)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),fς1+Fς1)−¯g(¯ϱ(¯∇ζη−¯∇ηζ),ς1)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,fς1+Fς1)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ς1)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς1)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς1)−¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς1), | (3.32) |
¯g([ζ,η],ς2)=¯g(¯ϱ[ζ,η],¯ϱς2)−¯g(¯ϱ[ζ,η],ς2)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),fς2+Fς2)−¯g(¯ϱ(¯∇ζη−¯∇ηζ),ς2)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,fς2+Fς2)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ς2)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,fς2)+¯g(hs(ζ,¯ϱη)−hs(η,¯ϱζ),Fς2)−¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,ς2), | (3.33) |
¯g([ζ,η],ϖ)=¯g(¯ϱ[ζ,η],¯ϱϖ)−¯g(¯ϱ[ζ,η],ϖ)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),¯ϱϖ)−¯g(¯ϱ(¯∇ζη−¯∇ηζ),ϖ)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,¯ϱϖ)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ϖ)=¯g(∇∗ζ¯ϱη−∇∗η¯ϱζ,¯ϱϖ)−¯g(h∗(ζ,¯ϱη)−h∗(η,¯ϱζ),ϖ), | (3.34) |
¯g([ζ,η],¯ϱϖ)=¯g(¯∇ζη−¯∇ηζ,¯ϱϖ)=¯g(¯∇ζη,¯ϱϖ)−¯g(¯∇ηζ,¯ϱϖ))=−¯g(¯ϱη,¯∇ζϖ)+¯g(¯ϱζ,¯∇ηϖ)=−¯g(¯∇ζϖ,¯ϱη)+¯g(¯∇ηϖ,¯ϱζ)=¯g(Aϖζ,¯ϱη)−¯g(Aϖη,¯ϱζ). | (3.35) |
The proof follows from (3.32)–(3.35).
Theorem 3.8. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, any slant distribution D′ (in particular D1,D2) is integrable iff
(i) ¯g(∇ζfη−AFηζ,¯ϱς)+¯g(∇ηfζ−AFζη,ς)=¯g(∇ζfη−AFηζ,ς)+¯g(∇ηfζ−AFζη,¯ϱς);
(ii) ¯g(∇ζfη−AFηζ,¯ϱϖ)+¯g(∇ηfζ−AFζη,ϖ)=¯g(∇ζfη−AFηζ,ϖ)+¯g(∇ηfζ−AFζη,¯ϱϖ);
(iii) ¯g(∇ζfη−AFηζ,ϖ)=¯g(∇ηfζ−AFζη,ϖ);
∀ζ,η∈Γ(D′) (in particular Γ(D1),Γ(D2)), ς∈Γ(D) and ϖ∈Γ(ltr(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. D′ is integrable iff
¯g([ζ,η],ς)=¯g([ζ,η],ϖ)=¯g([ζ,η],¯ϱϖ)=0, |
∀ζ,η∈Γ(D′) (in particular Γ(D1),Γ(D2)), ς∈Γ(D) and ϖ∈Γ(ltr(TO)). Then, from (2.3),(2.6),(2.8) and (3.1), we obtain
¯g([ζ,η],ς)=¯g(¯ϱ[ζ,η],¯ϱς)−¯g(¯ϱ[ζ,η],ς)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),¯ϱς)−¯g(¯ϱ(¯∇ζη−¯∇ηζ),ς)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,¯ϱς)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ς)=¯g(∇ζfη−AFηζ,¯ϱς)−¯g(∇ηfζ−AFζη,¯ϱς)−¯g(∇ζfη−AFηζ,ς)+¯g(∇ηfζ−AFζη,ς), | (3.36) |
¯g([ζ,η],ϖ)=¯g(¯ϱ[ζ,η],¯ϱϖ)−¯g(¯ϱ[ζ,η],ϖ)=¯g(¯ϱ(¯∇ζη−¯∇ηζ),¯ϱϖ)−¯g(¯ϱ(¯∇ζη−¯∇ηζ),ϖ)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,¯ϱϖ)−¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ϖ)=¯g(∇ζfη−AFηζ,¯ϱϖ)−¯g(∇ηfζ−AFζη,¯ϱϖ)−¯g(∇ζfη−AFηζ,ϖ)+¯g(∇ηfζ−AFζη,ϖ), | (3.37) |
¯g([ζ,η],¯ϱϖ)=¯g(¯∇ζ¯ϱη−¯∇η¯ϱζ,ϖ)=¯g(∇ζfη−AFηζ,ϖ)−¯g(∇ηfζ−AFζη,ϖ). | (3.38) |
The proof follows from (3.36)–(3.38).
This section includes the necessary and sufficient conditions for foliations determined by distributions on a bi-slant lightlike submanifold of a golden semi-Riemannian manifold to be totally geodesic.
Definition 4.1. [2] A bi-slant lightlike submanifold O of a golden semi-Riemannian manifold ¯O is said to be mixed geodesic if its second fundamental form h satisfies h(ζ,η)=0 for all ζ∈Γ(D1) and η∈Γ(D2). Thus, O is a mixed geodesic bi-slant lightlike submanifold if hl(ζ,η)=0 and hs(ζ,η)=0 for all ζ∈Γ(D1) and η∈Γ(D2).
Theorem 4.1. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, Rad(TO) defines a totally geodesic foliation iff
¯g(∇ζK1¯ϱP2ς+∇ζK2¯ϱP2ς−AL1¯ϱP3ςζ+∇ζL2¯ϱP3ς+∇ζ¯ϱP4ς+∇ζfP5ς−AFP5ςζ+∇ζfP6ς−AFP6ςζ,¯ϱη)=¯g(hl(ζ,K1¯ϱP2ς)+hl(ζ,K2¯ϱP2ς)+∇lζL1¯ϱP3ς+hl(ζ,L2¯ϱP3ς)+hl(ζ,¯ϱP4ς)+hl(ζ,fP5ς)+Dl(ζ,FP5ς)+hl(ζ,fP6ς)+Dl(ζ,FP6ς),η) |
∀ζ,η∈Γ(Rad(TO)) and ς∈Γ(S(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. The distribution Rad(TO) defines a totally geodesic foliation iff ∇ζη∈Γ(Rad(TO))∀ζ,η∈Γ(Rad(TO). ¯∇ being a metric connection and using (2.3), (2.6), (2.7), (2.8) and (3.1) ∀ζ,η∈Γ(Rad(TO) and ς∈Γ(S(TO)), we get
¯g(∇ζη,ς)=−¯g(η,¯∇ζς)=−¯g(¯ϱη,¯ϱ¯∇ζς)+¯g(¯ϱη,¯∇ζς)=−¯g(¯ϱη,¯ϱ¯∇ζς)−¯g(η,¯ϱ¯∇ζς)=−¯g(¯ϱη,¯∇ζ¯ϱP2ς+¯∇ζ¯ϱP3ς+¯∇ζ¯ϱP4ς+¯∇ζfP5ς+¯∇ζFP5ς+¯∇ζfP6ς+¯∇ζFP6ς)+¯g(η,¯∇ζ¯ϱP2ς+¯∇ζ¯ϱP3ς+¯∇ζ¯ϱP4ς+¯∇ζfP5ς+¯∇ζFP5ς+¯∇ζfP6ς+¯∇ζFP6ς), |
¯g(∇ζη,ς)=−¯g(∇ζK1¯ϱP2ς+∇ζK2¯ϱP2ς−AL1¯ϱP3ςζ+∇ζL2¯ϱP3ς+∇ζ¯ϱP4ς+∇ζfP5ς−AFP5ςζ+∇ζfP6ς−AFP6ςζ,¯ϱη)+¯g(hl(ζ,K1¯ϱP2ς)+hl(ζ,K2¯ϱP2ς)+∇lζL1¯ϱP3ς+hl(ζ,L2¯ϱP3ς)+hl(ζ,¯ϱP4ς)+hl(ζ,fP5ς)+Dl(ζ,FP5ς)+hl(ζ,fP6ς)+Dl(ζ,FP6ς),η). |
Thus, the theorem is completed.
Theorem 4.2. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, D defines a totally geodesic foliation iff
(i) ¯g(∇ζfς−AFςζ,¯ϱη)=¯g(∇ζfς−AFςζ,η);
(ii) ¯g(∇∗ζ¯ϱη,¯ϱϖ)=¯g(h∗(ζ,¯ϱη),ϖ);
(iii) h∗(ζ,¯ϱη) has no components in Γ(Rad(TO))
∀ζ,η∈Γ(D), ς∈Γ(D′)(in particular Γ(D1),Γ(D2)) where D′ is any slant distribution and ϖ∈Γ(ltr(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. The distribution D defines a totally geodesic foliation iff ∇ζη∈Γ(D), ∀ζ,η∈Γ(D). ¯∇ being a metric connection and using (2.3), (2.6), (2.8) and (3.1), ∀ζ,η∈Γ(D) and ς∈Γ(D′), we obtain
¯g(∇ζη,ς)=−¯g(η,¯∇ζς)=¯g(¯ϱη,¯∇ζς)−¯g(¯ϱη,¯ϱ(¯∇ζς))=¯g(η,¯ϱ(¯∇ζς))−¯g(¯ϱη,¯ϱ(¯∇ζς))=¯g(η,¯∇ζfς+¯∇ζFς)−¯g(¯ϱη,¯∇ζfς+¯∇ζFς), |
¯g(∇ζη,ς)=¯g(η,∇ζfς−AFςζ)−¯g(¯ϱη,∇ζfς−AFςζ). |
Now, from (2.3),(2.6) and (2.9), ∀ζ,η∈Γ(D) and ϖ∈Γ(ltr(TO)), we obtain
¯g(∇ζη,ϖ)=¯g(¯∇ζη,ϖ)=¯g(¯ϱ(¯∇ζη),¯ϱϖ)−¯g(¯ϱ(¯∇ζη),ϖ)=¯g(¯∇ζ¯ϱη,¯ϱϖ)−¯g(¯∇ζ¯ϱη,ϖ), |
¯g(∇ζη,ϖ)=¯g(∇∗ζ¯ϱη,¯ϱϖ)−¯g(h∗(ζ,¯ϱη),ϖ). |
Also, from (2.2),(2.6) and (2.9), ∀ζ,η∈Γ(D) and ϖ∈Γ(ltr(TO)), we obtain
¯g(∇ζη,¯ϱϖ)=¯g(¯∇ζ¯ϱη,ϖ), |
which implies
¯g(∇ζη,¯ϱϖ)=¯g(h∗(ζ,¯ϱη),ϖ), |
which completes the proof.
Theorem 4.3. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the slant distribution D′(in particular D1,D2) defines a totally geodesic foliation iff
(i) ¯g(fη,∇ζ¯ϱς)+¯g(Fη,hs(ζ,¯ϱς))=¯g(∇ζ¯ϱς,η);
(ii) ¯g(∇ζfη−AFηζ,¯ϱϖ)=¯g(∇ζfη−AFηζ,ϖ);
(iii) ∇ζfη−AFηζ has no components in Γ(Rad(TO))
∀ζ,η∈Γ(D′) (in particular Γ(D1),Γ(D2)), ς∈Γ(D) and ϖ∈Γ(ltr(TO)).
Proof. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. The distribution D′ defines a totally geodesic foliation iff ∇ζη∈Γ(D′)∀ζ,η∈Γ(D′). ¯∇ being a metric connection and using (2.3), (2.6) and (3.1), ∀ζ,η∈Γ(D′) and ς∈Γ(D), we obtain
¯g(∇ζη,ς)=−¯g(η,¯∇ζς)=¯g(¯ϱη,¯∇ζς)−¯g(¯ϱη,¯ϱ(¯∇ζς))=¯g(η,¯∇ζ¯ϱς)−¯g(fη+Fη,¯∇ζ(¯ϱς)), |
which implies
¯g(∇ζη,ς)=¯g(η,∇ζ¯ϱς)−¯g(fη,∇ζ¯ϱς)−¯g(Fη,hs(ζ,¯ϱς)). |
Now, from (2.3), (2.6), (2.8) and (3.1), ∀ζ,η∈Γ(D′) and ϖ∈Γ(ltr(TO)), we obtain
¯g(∇ζη,ϖ)=¯g(¯∇ζη,ϖ)=¯g(¯ϱ(¯∇ζη),¯ϱϖ)−¯g(¯ϱ(¯∇ζη),ϖ)=¯g(¯∇ζ¯ϱη,¯ϱϖ)−¯g(¯∇ζ¯ϱη,ϖ), |
which implies
¯g(∇ζη,ϖ)=¯g(∇ζfη−AFηζ,¯ϱϖ)−¯g(∇ζfη−AFηζ,ϖ). |
Now, from (2.2), (2.6), (2.8) and (3.1), ∀ζ,η∈Γ(D′) and ϖ∈Γ(ltr(TO)), we obtain
¯g(∇ζη,¯ϱϖ)=¯g(¯∇ζη,¯ϱϖ)=¯g(¯ϱ(¯∇ζη),ϖ)=¯g(¯∇ζ¯ϱη,ϖ)=¯g(¯∇ζfη+¯∇ζFη,ϖ), |
which gives
¯g(∇ζη,¯ϱϖ)=¯g(∇ζfη−AFηζ,ϖ). |
This completes the proof.
Theorem 4.4. Let O be a mixed geodesic bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, the slant distribution D′(in particular D1,D2) defines a totally geodesic foliation iff
(i) ¯g(fη,∇ζ¯ϱς)=¯g(η,∇ζ¯ϱς);
(ii) ¯g(∇ζ¯ϱϖ,fη)+¯g(hs(ζ,¯ϱϖ),Fη)=¯g(∇ζ¯ϱϖ,η);
(iii) ∇ζfη−AFηζ has no components in Γ(Rad(TO))
∀ζ,η∈Γ(D′) (in particular Γ(D1),Γ(D2)), ς∈Γ(D) and ϖ∈Γ(ltr(TO)).
Proof. Let O be a mixed geodesic bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O, we have hs(ζ,¯ϱς)=0, ∀ζ∈Γ(D′) and ς∈Γ(D). The distribution D′ defines a totally geodesic foliation iff ∇ζη∈Γ(D′). ¯∇ being a metric connection and using (2.3), (2.6) and (3.1), ∀ζ,η∈Γ(D′) and ς∈Γ(D), we obtain
¯g(∇ζη,ς)=−¯g(η,¯∇ζς)=¯g(¯ϱη,¯∇ζς)−¯g(¯ϱη,¯ϱ(¯∇ζς))=¯g(η,¯∇ζ¯ϱς)−¯g(fη+Fη,¯∇ζ(¯ϱς))=¯g(η,∇ζ¯ϱς)−¯g(fη,∇ζ¯ϱς)−¯g(Fη,hs(ζ,¯ϱς)), |
which implies
¯g(∇ζη,ς)=¯g(η,∇ζ¯ϱς)−¯g(fη,∇ζ¯ϱς). |
From (2.3), (2.6) and (3.1), ∀ζ,η∈Γ(D′) and ϖ∈Γ(ltr(TO)), we obtain
¯g(∇ζη,ϖ)=−¯g(η,¯∇ζϖ)=¯g(¯ϱη,¯∇ζϖ)−¯g(¯ϱη,¯ϱ(¯∇ζϖ))=¯g(η,¯∇ζ¯ϱϖ)−¯g(fη+Fη,¯∇ζ(¯ϱϖ))=¯g(η,∇ζ¯ϱϖ)−¯g(fη,∇ζ¯ϱϖ)−¯g(Fη,hs(ζ,¯ϱϖ)), |
which implies
¯g(∇ζη,ϖ)=¯g(∇ζ¯ϱϖ,η)−¯g(∇ζ¯ϱϖ,fη)−¯g(hs(ζ,¯ϱϖ),Fη). |
Now, from (2.2), (2.6), (2.8) and (3.1), ∀ζ,η∈Γ(D′) and ϖ∈Γ(ltr(TO)), we obtain
¯g(∇ζη,¯ϱϖ)=¯g(¯∇ζη,¯ϱϖ)=¯g(¯ϱ(¯∇ζη),ϖ)=¯g(¯∇ζ¯ϱη,ϖ)=¯g(¯∇ζfη+¯∇ζFη,ϖ), |
which gives
¯g(∇ζη,¯ϱϖ)=¯g(∇ζfη−AFηζ,ϖ). |
This completes the proof.
Theorem 4.5. Let O be a bi-slant lightlike submanifold of a golden semi-Riemannian manifold ¯O. Then, O is mixed geodesic iff the following holds
(i) F(∇ζfς−AFςζ)=−C(hs(ζ,fς)+∇sζFς);
(ii) hl(ζ,fς)+Dl(ζ,Fς)=hs(ζ,fς)+∇sζFς
∀ζ∈Γ(D) and ς∈Γ(D′) (in particular Γ(D1),Γ(D2)).
Proof. From (2.5), (2.6), (2.8), (3.1), (3.2) and (3.3), we obtain
h(ζ,ς)=¯∇ζς−∇ζς=¯ϱ(¯ϱ¯∇ζς)−¯ϱ(¯∇ζς)−∇ζς=¯ϱ(¯∇ζ¯ϱς)−(¯∇ζ¯ϱς)−∇ζς=¯ϱ(¯∇ζfς+¯∇ζFς)−(¯∇ζfς+¯∇ζFς)−∇ζς=¯ϱ(∇ζfς+hl(ζ,fς)+hs(ζ,fς)−AFςζ+∇sζFς+Dl(ζ,Fς))−(∇ζfς+hl(ζ,fς)+hs(ζ,fς)−AFςζ+∇sζFς+Dl(ζ,Fς))−∇ζς. |
Taking transversal part of above equation, we get
h(ζ,ς)=F(∇ζfς−AFςζ)+C(hs(ζ,fς)+∇sζFς)−hl(ζ,fς)−hs(ζ,fς)−∇sζFς−Dl(ζ,Fς). |
Hence, h(ζ,ς)=0, iff (i) and (ii) hold, which completes the proof.
We investigate some interesting results on bi-slant lightlike submanifolds of golden semi-Riemannian manifolds and give two examples on such submanifolds. We also discuss the integrability of distributions on bi-slant lightlike submanifolds. Certain conditions on foliations determined by distributions on bi-slant lightlike submanifolds of golden semi-Riemannian manifolds are derived.
The authors declare they have not used Artificial Intelligence (AI) tools in the creation of this article.
The authors are grateful to the referees and the editor for their valuable suggestions and remarks that definitely improve the paper. The author, Fatemah Mofarreh, expresses her gratitude to Princess Nourah bint Abdulrahman University Researchers Supporting Project number (PNURSP2023R27), Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia. The authors Muqeem Ahmad and Mobin Ahmad would like to thank Integral University, Lucknow, India, for providing the manuscript number IU/R & D/2022-MCN0001737 for the present research work.
The authors declare no conflict of interest.
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