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S. G. Elgendi

Publications and source records attributed to S. G. Elgendi.

At least 19 recordsLinked to original sources
arXiv2025

The existence and uniqueness of Hashiguchi connection in KG-approach

In this study, we treat intrinsic Finsler geometry using the Klein-Grifone approach (KG-approach). A uniqueness and existence theorem for the Hashiguchi connection on a Finsler manifold is investigated intrinsically (in coordinate-free fashion). Calculations are made for the Hashiguchi connection's torsion and curvature tensors. Some properties are examined, together with the Bianchi identities of the associated curvature and torsion tensors. An overview of the four fundamental linear connections in Finsler geometry in the KG-approach is provided globally for comparison's sake and completeness.

math.DG↗
arXiv2025

Vacuum Homogeneous and Nonhomogeneous Metrics with Conventional and Quantized Metric Tensor: Singular or Nonsingular Solution

To investigate whether the Universe underwent a singularity or maintained a nonsingular state, we carry out analytical and numerical analyses of the evolution of the Raychaudhuri equations in vacuum, alongside homogeneous and nonhomogeneous cosmic backgrounds. The results obtained from the Schwarzschild, Friedmann--Lemaitre--Robertson--Walker (FLRW), and Einstein--Gilbert--Straus (EGS) metrics are systematically compared. Analyzing the results from both, conventional and quantized metric tensor, it revealed insights into the nature of initial and spatial singularities. Results associated with the Schwarzschild metric demonstrate a positive evolution that corresponds with a reduction in radial distance (nonsingularity). In contrast, the proposed quantization reverses this trend, leading to a negative evolution (singularity). The situation is similar for the FLRW metric, where the suggested quantization results in a positive evolution as cosmic time decreases, in contrast to the classical and conventional metrics, which are associated with negative evolution. The analysis of the EGS metric reveals that classical evolution remains positively oriented, particularly with a reduction in radial distance. Moreover, the introduction of quantized and conventional metric tensors fully retrains the cosmic time dependence. The results obtained are a rightful recognition of the substantial efforts dedicated to the establishment of the Swiss-cheese model, demonstrating that the EGS metric indeed facilitates the temporal and spatial development of our Universe.

gr-qc↗
arXiv2025

Special anisotropic conformal changes of conic pseudo-Finsler surfaces

This study presents many special anisotropic conformal changes of a conic pseudo-Finsler surface $(M,F)$, such as $C$-anisotropic and horizontal $C$-anisotropic conformal transformations, which reduce to $C$-conformal when the conformal factor is solely position-dependent. Furthermore, we present vertical $C$-anisotropic conformal changes and demonstrate that they are characterized by the property of $(M,F)$ being Riemannian. Additionally, we examine the anisotropic conformal transformation that fulfils the $ϕT$-condition, the horizontal $ϕT$-condition, and the vertical $ϕT$-condition. The first two conditions reduce to the $\boldsymbolσ T$-condition when the conformal factor relies solely on a positional variable. We demonstrate that, under the vertical $ϕT$-condition change, every Landsberg surface is Berwaldian. Thus, the vertical $ϕT$-condition is equivalent to the $T$-condition. Furthermore, we examine the scenario when the anisotropic conformal factor becomes the main scalar of the non-Riemannian surface $(M,F)$. We present an example of a Finslerian Schwarzschild-de Sitter solution having Finslerian spherical symmetry and apply our results to it.

math.DG↗
arXiv2025

Anisotropic conformal change of conic pseudo-Finsler surfaces, II

This paper is a continuation of our investigation of the anisotropic conformal change of a conic pseudo-Finsler surface $(M,F)$, namely, the change $\overline{F}(x,y)=e^{ϕ(x,y)}F(x,y)$ \cite{first paper}. We obtain the relationship between some important geometric objects of $F $ and their corresponding objects of $\overline{F}$, such as Berwald, Landsberg and Douglas tensors, as well as the T-tensor. In contrast to isotropic conformal transformation, under an anisotropic conformal transformation, we find out the necessary and sufficient conditions for a Riemannian surface to be anisotropically conformal transformed to Berwald or Landsberg or Douglas surfaces. Consequently, we determine under what condition the geodesic spray of a two-dimensional pseudo-Berwald metric $\overline{F}$ is Riemann metrizable by a two-dimensional pseudo-Riemannian metric $F$. We show an example of a conformal transformation of a Riemannian metric $F$ that is not geodesically equivalent to a Riemannian metric but is instead Berwaldian. Also, we determine the necessary and sufficient conditions for $F $ to be anisotropically conformally flat (i.e., $\overline{F}$ is Minkowskian). Moreover, we identify the required conditions for preserving the $T$-condition under an anisotropic conformal change. Finally, we establish the necessary conditions for a Riemannian metric to be anisotropically conformal to a Douglas metric.

math.DG↗
arXiv2024

On the covariant coefficients of geodesic sprays on Finsler manifolds

For a Finsler metric $F$, we introduce the notion of $F$-covariant coefficients $H_i$ of the geodesic spray of $F$ (Def. 3.1). We study some geometric consequences concerning the objects $H_i$. If the $F$-covariant coefficients $H_i$ are written in the form $H_i={\dot{\partial}}_iH$, for some smooth function $H$ on ${\mathcal T\hspace{-1pt}M}$, positively 3-homogeneous in y, then $H$ is called spray scalar or simply $S$-scalar. We prove that if the $S$-scalar exists, then it is of the form $H=\frac{1}{12}\,y^i\partial_iF^2$ and this expression is unique up to a function of position only. We prove also that on a Finsler maifold $(M,F)$, the $S$-scalar $H$ exists if and only if $(M,F)$ is dually flat. Generally, the $n^3$ functions $H^h_{ij}$ resulting from the $F$-covariant coefficients do not form a linear connection. We find out that in the case of projectively flat metrics, the $n^3$ functions $H^h_{ij}$ are coefficients of a linear connection. We introduce two new special Finsler spaces, namely, the $H$-Berwald and the $H$-Landsberg spaces and show that every $H$-Berwald metric is $H$-Landsbergian but the converse is not necessarily true. Also, we study the $F$-covariant coefficients $H_i$ of projectivly flat and dually flat spherically symmetric Finsler metrics and provide a solution of the "$H$-unicorn" Landsberg problem. Finally, we give some examples of $H$-Berwald and $H$-Landsberg metrics and an example of $H$-Landsberg metric which is not $H$-Berwaldian.

math.DG↗
arXiv2024

On Riemann curvature of spherically symmetric metrics

In this paper, studying the inverse problem, we establish a curvature compatibility condition on a spherically symmetric Finsler metric. As an application, we characterize the spherically symmetric metrics of scalar curvature. We construct a Berwald frame for a spherically symmetric Finsler surface and calculate some associated geometric objects. Several examples are provided and discussed. Finally, we give a note on a certain general $(α,β)$-metric that appears in the literature.

math.DG↗
arXiv2024

Anisotropic conformal change of conic pseudo-Finsler surfaces, I

The present work is devoted to investigate anisotropic conformal transformation of conic pseudo-Finsler surfaces $(M,F)$, that is, $ F(x,y)\longmapsto \overline{F}(x,y)=e^{ϕ(x,y)}F(x,y)$, where the function $ϕ(x,y)$ depends on both position $x$ and direction $y$, contrary to the ordinary (isotropic) conformal transformation which depends on position only. If $F$ is a pseudo-Finsler metric, the above transformation does not yield necessarily a pseudo-Finsler metric. Consequently, we find out necessary and sufficient condition for a (conic) pseudo-Finsler surface $(M,F)$ to be transformed to a (conic) pseudo-Finsler surface $(M,\overline{F})$ under the transformation $\overline{F}=e^{ϕ(x,y)}F$. In general dimension, it is extremely difficult to find the anisotropic conformal change of the inverse metric tensor in a tensorial form. However, by using the modified Berwald frame on a Finsler surface, we obtain the change of the components of the inverse metric tensor in a tensorial form. This progress enables us to study the transformation of the Finslerian geometric objects and the geometric properties associated with the transformed Finsler function $\overline{F}$. In contrast to isotropic conformal transformation, we have a non-homothetic conformal factor $ϕ(x,y)$ that preserves the geodesic spray. Also, we find out some invariant geometric objects under the anisotropic conformal change. Furthermore, we investigate a sufficient condition for $\overline{F}$ to be dually flat or/and projectively flat. Finally, we study some special cases of the conformal factor $ϕ(x,y)$. Various examples are provided whenever the situation needs.

math.DG↗
arXiv2021

$(α,β)$-metrics satisfying the $T$-Condition or the $σT$-Condition

We describe the $(α,β)$-metrics whose the $T$-tensor vanishes ($T$-condition) and the $(α,β)$-metrics that satisfy the $σT$-condition $σ_hT^h_{ijk}=0$, where $σ_h=\frac{\partial σ}{\partial x^h}$ and $σ$ is a smooth function on $M$. These classes have already been obtained by Z. Shen and G. S. Asanov in a completely different approach. The Finsler metrics of the first class are Berwaldian, the metrics of the second class are almost regular non-Berwaldian Landsberg metrics.

math.DG↗
arXiv2021

On the classifiation of Landsberg spherically symmetric Finsler metrics

In this paper, as an application of the inverse problem of calculus of variations, we investigate two compatibility conditions on the spherically symmetric Finsler metrics. By making use of these conditions, we focus our attention on the Landsberg spherically symmetric Finsler metrics. We classify all spherically symmetric manifolds of Landsberg or Berwald types. For the higher dimensions $n\geq 3$, we prove that: all Landsberg spherically symmetric manifolds are either Riemannian or their geodesic sprays have a specific formula; all regular Landsberg spherically symmetric metrics are Riemannian; all (regular or non-regular) Berwald spherically symmetric metrics are Riemannian. Moreover, we establish new unicorns, i.e., new explicit examples of non-regular non-Berwaldian Landsberg metrics are obtained. For the two-dimensional case, we characterize all Berwald or Landsberg spherically symmetric surfaces.

math.DG↗
arXiv2019

Solutions for the Landsberg unicorn problem in Finsler geometry

It is still a long-standing open problem in Finsler geometry, is there any regular Landsberg metric which is not Berwaldian. However, there are non-regular Landsberg metrics which are not Berwladian. The known examples are established by G. S. Asanov and Z. Shen. In this paper, we use the Maple program to study some explicit examples of non-Berwaldian Landsberg metrics. In fact, such kinds of examples are very tedious and complicated to investigate. Nonetheless, we use the maple program and Finsler packages to simplify the calculations in an elegant way. Depending on these examples, we manage to figure out some geometric properties of the geodesic spray of a non-Berwaldain Landsberg metric. Deforming this spray in a very specific way, using the metrizability tools of the deformed spray, we get new (very simple) non-Berwaldian Landsberg metrics. Moreover, the powerful of this procedure is investigating a very simple and useful formula for the general class obtained by Z. Shen.

math.DG↗
arXiv2018

Coordinate-free study of Finsler spaces of $H_{p}$-scalar curvature

The aim of the present paper is to provide an \emph{intrinsic} investigation of special Finsler spaces of $H_{p}$-scalar curvature and of $H_{p}\,$-constant curvature. Characterizations of such spaces are shown. Sufficient condition for Finsler space of $H_{p}$-scalar curvature to be of perpendicular scalar curvature is investigated. Necessary and sufficient condition under which a Finsler space of scalar curvature turns into a Finsler space of $H_{p}$-scalar curvature is given. Further, certain conditions under which a Finsler manifolds of $H_{p}$-scalar curvature and of scalar curvature reduce to a Finsler manifold of $H_{p}$-constant curvature are obtained. Finally, various examples are studied and constructed.

math.DG↗
arXiv2018

One form deformation of sprays

In this paper, we introduce the notion of one form deformation of sprays. The metrizability of the new spray, when the background spray is flat, is characterized. Therefore, we obtain new projectively flat metrics of constant flag curvature $1$. Moreover, these new metrics are not, generally, isometric to the Klein metric via affine transformations. New solutions for Hilbert's fourth problem are obtained and constructed. Various examples are discussed and studied.

math.DG↗
arXiv2018

Semi Concurrent vector fields in Finsler geometry

In the present paper, we introduce and investigate the notion of a semi concurrent vector field on a Finsler manifold. We show that some special Finsler manifolds admitting such vector fields turn out to be Riemannian. We prove that Tachibana's characterization of Finsler manifolds admitting a concurrent vector field leads to Riemannain metrics. We give an answer to the question raised in \cite{DWF}: "Is any n-dimensional Finsler manifold $(M,F)$, admitting a non-constant smooth function $f$ on $M$ such that $\frac{\partial f}{\partial x^i}\frac{\partial g^{ij}}{\partial y^k}=0$, a Riemannian manifold?". Various examples for conic Finsler and Riemannian spaces that admit semi-concurrent vector field are presented. Finally, we conjectured that there is no regular Finsler non-Riemannian metric that admits a semi-concurrent vector field. In other words, a Finsler metric admitting a semi-concurrent vector field is necessarily either Riemannian or conic Finslerian.

math.DG↗
arXiv2018

On the problem of non Berwaldian Landsberg spaces

In this paper, we study the long existence problem of non Berwaldian Landsberg spaces using the conformal transformation point of view. Under conformal transformation, the Berwald and Landesberg tensors are calculated in terms of the T-tensor. By giving examples, we show that under conformal transformation, there are Landsberg spaces with non-vanishing T-tensor. A necessary condition for a Landsberg space to be Berwaldian is given. Various special cases are studied. Cases in which the Landsberg spaces can not be Berwaldian are shown. Examples of non-Berwaldian landsberg (singular) spaces are given.

math.DG↗
arXiv2015

Nullity distributions associated with Chern connection

The nullity distributions of the two curvature tensors \, $\overast{R}$ and $\overast{P}$ of the Chern connection of a Finsler manifold are investigated. The completeness of the nullity foliation associated with the nullity distribution $\N_{R^\ast}$ is proved. Two counterexamples are given: the first shows that $\N_{R^\ast}$ does not coincide with the kernel distribution of \, $\overast{R}$; the second illustrates that $\N_{P^\ast}$ is not completely integrable. We give a simple class of a non-Berwaldian Landsberg spaces with singularities.

math.DG↗
arXiv2014

Computing nullity and kernel vectors using NF-package: Counterexamples

A computational technique for calculating nullity vectors and kernel vectors, using the new Finsler package, is introduced. As an application, three interesting counterexamples are given. The first counterexample shows that the two distributions $\mathrm{Ker}_R$ and $\N_R$ do not coincide. The second shows that the nullity distribution $\N_{P^\circ}$ is not completely integrable. The third shows that the nullity distribution $\N_\mathfrak{R}$ is not a sub-distribution of the nullity distribution $\N_{R^\circ}$.

math.DG↗
arXiv2014

Existence and uniqueness of Chern connection in the Klein-Grifone approach

The Klein-Grifone approach to global Finsler geometry is adopted. A global existence and uniqueness theorem for Chern connection is formulated and proved. The torsion and curvature tensors of Chern connection are derived. Some properties and the Bianchi identities for this connection are investigated. A concise comparison between Berwald, Cartan and Chern connections is presented.

math.DG↗