- 1Department of Mathematics, College of Science, King Khalid University, Abha, Saudi Arabia
- 2Department of Mathematics, University of Tabuk, Tabuk, Saudi Arabia
- 3Department of Mathematics, Sri Venkateswara College, University of Delhi, New Delhi, India
- 4Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah, Saudi Arabia
This study attempts to establish new upper bounds on the mean curvature and constant sectional curvature of the first positive eigenvalue of the ψ − Laplacian operator on Riemannian manifolds. Various approaches are being used to find the first eigenvalue for the ψ − Laplacian operator on closed oriented bi-slant submanifolds in a Sasakian space form. We extend different Reilly-like inequalities to the ψ − Laplacian on bi-slant submanifolds in a unit sphere depending on our results for the Laplacian operator. The conclusion of this study considers some special cases as well.
1 Introduction
It is one of the most significant aspects of Riemannian geometry to determine the bounds of the Laplacian on a given manifold. One of the major objectives is to find the eigenvalue that arises as a solution of the Dirichlet or Neumann boundary value problems for curvature functions. Because different boundary conditions exist on a manifold, one can adopt a theoretical perspective to the Dirichlet boundary condition using the upper bound for the eigenvalue as a technique of analysis for the Laplacian’s appropriate bound on a given manifold. Assessing the eigenvalue for the Laplacian and ψ − Laplacian operators has been progressively well-known over a long time. The generalization of the usual Laplacian operator, which is an anisotropic mean curvature, was studied in [17]. Let K denote a complete noncompact Riemannian manifold and B signify the compact domain within K. Let λ1(B) > 0 be the first eigenvalue of the Dirichlet boundary value problem.
where Δ represents the Laplacian operator on the Riemannian manifold Km. The Reilly’s formula deals exclusively with the fundamental geometrical characteristics of a given manifold. This is generally acknowledged by the following statement. Let (Km, g) be a compact m − dimensional Riemannian manifold and λ1 denote the first nonzero eigenvalue of the Neumann problem.
where η is the outward normal on ∂Km.
As a result of Reilly [24], we have the following inequality for a manifold Km immersed in a Euclidean space with ∂Km = 0
where H is the mean curvature vector of immersion Km into Rn,
Zeng and He computed the upper bounds for the ψ − Laplace operator as it relates to the first eigenvalue for Finsher submanifolds in Minkowski space. The first eigenvalue of the Laplace operator on a closed manifold was described by Seto and Wei . Nevertheless, Du et al. [16] derived the generalized Reilly inequality and calculated the first nonzero eigenvalue of the ψ − Laplace operator. By adopting a very similar strategy, Blacker and Seto [3] demonstrated a Lichnero-type lower limit for the first nonzero eigenvalue of the ψ − Laplacian for Neumann and Dirichlet boundary conditions.
The studies [14, 15] illustrate the first nonnull Laplacian eigenvalue, which is considered an extension of Reilly’s work . The results of the distinct classes of Riemannian submanifolds for diverse ambient spaces show that the results of both first nonzero eigenvalues portray similar inequality and have the same upper bounds [13, 14]. In the case of the ambient manifold, it is known from past research that Laplace and ψ − Laplace operators on Riemannian manifolds played a vital role in accomplishing different achievements in Riemannian geometry (see [2, 5, 10, 11, 17, 22, 23,]).
The ψ − Laplacian on a m − dimensional Riemannian manifold Km is defined as
where ψ > 1 and if ψ = 2; then, the abovementioned formula becomes the usual Laplacian operator.
The eigenvalue of Δh, on the other hand, is Laplacian-like. If a function h ≠ 0 meets the following equation with Dirchilet boundary condition or Neumann boundary condition as discussed earlier
where λ is a real number called the Dirichlet eigenvalue. In the same way, the previous requirements apply to the Neumann boundary condition.
Looking at Riemannian manifolds without boundaries, the Reilly-type inequality for the first nonzero eigenvalue λ1,ψ for ψ − Laplacian was computed in .
On the other hand, Chen was the first to propose the geometry of slant immersions as a logical extension of both holomorphic and totally real immersions. In addition, Lotta introduced the notion of slant submanifolds within the context of almost contact metric manifolds, and Cabrerizo et al. [9] delved more into these submanifolds. More precisely, Cabrerizo et al. explored slant submanifolds in the setting of Sasakian manifolds. However, Cabrerizo et al. introduced another generalization of slant and contact CR-submanifolds; that is, they proposed the idea of bi-slant and semi-slant submanifolds in the almost contact metric manifolds and provided several examples of these submanifolds.
After examining the literature, a logical question arises: can the Reilly-type inequalities for submanifolds of spheres be obtained using almost contact metric manifolds, as described in [1, 14, 15]? To answer this question, we explore the Reilly-type inequalities for bi-slant submanifolds isometrically immersed in a Sasakian space form
2 Preliminaries
A (2n + 1) − dimensional C∞ − manifold
The manifold
for all
An almost contact metric manifold
for any
A Sasakian manifold
for all vector fields e1, e2, e3 on
K is assumed to be a submanifold of an almost contact metric manifold
for each e1, e2 ∈ TK and v ∈ T⊥K, where σ and Av are the second fundamental form and the shape operator, respectively, for the immersion of K into
where g is the Riemannian metric on
If Te1 and Ne1 represent the tangential and normal part of ϕe1, respectively, for any e1 ∈ TK, we can write
Similarly, for any v ∈ T⊥K, we write
where tv and nv are the tangential and normal parts of ϕv, respectively. Thus, T (resp. N) is 1-1 tensor field on TK (resp. T⊥K) and t (resp. n) is a tangential (resp. normal) valued 1-form on T⊥K (resp. TK).
The notion of slant submanifolds in contact geometry was first defined by A. Lotta . Later, these submanifolds were studied by Cabrerizo et al. [9]. Now, we have the following definition of slant submanifolds:
Definition
A submanifold K of an almost contact metric manifold
Moreover, Cabrerizo et al. [9] proved the characterizing equation for the slant submanifold. More precisely, they proved that a submanifold Nm is said to be a slant submanifold if ∃ a constant τ ∈ [0, 1] and a (1, 1) tensor field T, which satisfies the following relation:
where τ = − cos2α.
From (2.10), it is easy to conclude the following:
Now, we define the bi-slant submanifold, which was introduced by Cabrerizo et al. .
A submanifold K of an almost contact metric manifold
1)
2) The distribution
3) The distribution
If α1 = 0 and α2 = π/2, then the bi-slant submanifold is a semi-invariant submanifold. Now, we have the following example of a bi-slant submanifold:
Example.
Considering the 5-dimensional submanifold in R9 with the usual Sasakian structure, such that
for any α1, α2 ∈ (0, π/2), then it is easy to see that this is an example of a bi-slant submanifold M in R9 with slant angles α1 and α2. Moreover, it can be observed that
form a local orthonormal frame of TK, in which
It is assumed that Kd=2p+2q+1 is a bi-slant submanifold of dimension d in which 2p and 2q are the dimensions of the slant distributions
The dimension of the bi-slant submanifold Kd can be decomposed as d = 2p + 2q + 1; then, using the formula (2.10) for slant distributions, we have
and
Then
The relation (2.12) implies that
From the relation (2.13) and Gauss equation we have
or
In the study [1], Ali et al. studied the effect of conformal transformation on the curvature and second fundamental form. More precisely, it is assumed that
where ρa is the component of the covariant derivative of ρ along the vector ea, that is, dρ = ∑aρaea.
Applying the pullback property in (2.15) to Km via the point x, we get
where
The following significant relation was proved in [1].
3 Main Results
Initially, some basic results and formulas will be discussed which are compatible with the studies ([1, 22]).
It is well-known that a simply connected Sasakian space form
Now, we have the following result, which is based on the preceding arguments:
Lemma 3.1. [1] Let Kd be a slant submanifold of a Sasakian space form
for ψ > 1.Remark: The Lemma 3.1 is also true for the bi-slant submanifolds and can be proved on the same lines as derived in [1].In the next result, we obtain a result which is analogous to Lemma 2.7 of [22]. Indeed, in Lemma 3.1 by the application of test function, we obtain the higher bound for λ1,ψ in terms of conformal function.
Proposition 3.2. Let Kd be a d − dimensional bi-slant submanifold which is closed orientable isometrically immersed in a Sasakian space form
where x is the conformal map used in Lemma 3.1, and ψ > 1. The standard metric is identified by Lc,, and we consider x*L1 = e2pLc.Proof: Considering Ωa as a test function, along with Lemma 3.1, we have
Observing that
On using 1 < ψ ≤ 2, we conclude
By the application of Holder’s inequality together with (3.2).–.(3.4), we get
which is (3.1). On the other hand, if we assume ψ ≥ 2, then by Holder inequality
As a result, we get
The Minkowski inequality provides
By the application of 3.2, 3.7, and .3.8, it is easy to get (3.1).In the next theorem, we are going to provide a sharp estimate for the first eigenvalue of the ψ − Laplace operator on the bi-slant submanifold of the Sasakian space form
Theorem 3.3. Let Kd be a d − dimensional bi-slant submanifold of a Sasakian space form
for 1 < ψ ≤ 2 and
for
Proof
We can calculate e2ρ with the help of conformal relations and the Gauss equation. Let
On tracing (2.16), we have
Using 3.12, 3.13, and 3.14, we get
The abovementioned relation implies that
Furthermore, on simplification, we get
On integrating along dV, it is easy to see that
which is equivalent to (3.9). If ψ > 2, then it is not possible to apply Holder inequality to govern
From the assumption, it is evident that d ≥ 2ψ − 2. On applying Young’s inequality, we arrive at
From Eqs 3.20, 3.21, we conclude the following:
Substituting (3.22) in (3.1), we obtain (3.10). For the bi-slant submanifolds, the equality case holds true in (3.9), and the equality cases of (3.2) and 3.4 imply that
for a = 1, … , 2t + 2. For 1 < ψ < 2, we have |Ωa| = 0 or 1. Therefore, there exists only one a for which |Ωa| = 1 and λ1,ψ = 0, which is not possible since the eigenvalue λi,ψ ≠ 0. This leads to using the value of ψ equal to 2, so we can apply Theorem 1.5 of [15].For ψ > 2, the equality in (3.10) still holds; this indicates that equalities in (3.7) and (3.8) are satisfied, and this leads to
and there exists a such that |∇Ωa| = 0. It shows that Ωa is a constant and λ1,ψ = 0; this again contradicts the fact that λ1,ψ ≠ 0, which completes the proof.Note 3.1 If ψ = 2, then the ψ − Laplacian operator becomes the Laplacian operator. Therefore, we have the following corollary.
Corollary 3.4. Let Kd be a d − dimensional bi-slant submanifold of a Sasakian space form
By the application of Theorem 3.3 for 1 < ψ ≤ 2, we have the following result.
Theorem 3.5. Let Kd be a d − dimensional bi-slant submanifold of a Sasakian space form
for 1 < ψ ≤ 2.Proof: If 1 < ψ ≤ 2, we have
On combining (3.9) and (3.25), we get the required inequality. This completes the proof.Note 3.2 If κ = 1, then simply the connected Sasakian space form
for 1 < ψ ≤ 2 and
for
for 1 < ψ ≤ 2 and
for
Furthermore, by Corollary 3.4 and Note 3.1, we deduce the following.Corollary 3.8 Let Kd be a d − dimensional semi-invariant submanifold of a Sasakian space form
In addition, we also have the following corollary, which can be derived from Theorem 3.5.Corollary 3.9 Let Kd be a d − dimensional semi-invariant submanifold of a Sasakian space form
for 1 < ψ ≤ 2.
Data Availability Statement
The original contributions presented in the study are included in the article/Supplementary Material, further inquiries can be directed to the corresponding author.
Author Contributions
All the authors listed have made a substantial, direct, and intellectual contribution to the work and approved it for publication.
Funding
The first author extends his appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through research groups program under grant number R.G.P.1/206/42.
Conflict of Interest
The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
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Keywords: eigenvalues, Laplacian, bi-slant submanifolds, Sasakian space form, Reilly-like inequalities
Citation: Alkhaldi AH, Khan MA, Aquib M and Alqahtani LS (2022) Estimation of Eigenvalues for the ψ-Laplace Operator on Bi-Slant Submanifolds of Sasakian Space Forms. Front. Phys. 10:870119. doi: 10.3389/fphy.2022.870119
Received: 05 February 2022; Accepted: 10 March 2022;
Published: 18 May 2022.
Edited by:
Josef Mikes, Palacký University, CzechiaReviewed by:
Anouar Ben Mabrouk, University of Kairouan, TunisiaAligadzhi Rustanov, Moscow State Pedagogical University, Russia
Copyright © 2022 Alkhaldi, Khan, Aquib and Alqahtani. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Ali H. Alkhaldi, ahalkhaldi@kku.edu.sa; Meraj Ali Khan, meraj79@gmail.com