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Nurettin Cenk Turgay

Publications and source records attributed to Nurettin Cenk Turgay.

At least 19 recordsLinked to original sources
arXiv2026

Hypersurfaces with Non-diagonalizable Shape Operators in Minkowski Spaces

In this paper, we study hypersurfaces $M^4$ in the Minkowski space $\mathbb{E}^5_1$ whose shape operator $S$ is non-diagonalizable, having a triple real eigenvalue $λ$ with a one-dimensional eigenspace together with a simple eigenvalue $μ$ (Case~(iii) in the classification of Magid). Assuming that $λ$ and $μ$ satisfy a functional relation $λ=f(μ)$ and that the eigenvector field of $μ$ is geodesic, we show that $λ$ and $μ$, as well as the pseudo-orthonormal frame, are intrinsic invariants of $M$, determined by the induced metric up to sign. As a consequence, we prove that such hypersurfaces are unique up to isometries of $\mathbb{E}^5_1$. We also obtain a classification of the warped product hypersurfaces of this type.

math.DG↗
arXiv2026

On Time-Like Class A Surfaces of a Warped Space-time with Lorentzian Fiber

In this paper, we consider time-like surfaces in the static space-time given by the warped product $\mathbb L^3_1(c)\, _f\times (I,dz^2)$, where $\mathbb L^3_1(c)$ denotes the Lorentzian space form with the constant sectional curvature $c\in\{-1,0,1\}$. In particular, we study the surfaces with light-like $\left(\frac{\partial}{\partial z}\right)^T$. First, we construct a globally defined pseudo-orthonormal frame field on a surface satisfying this condition and deal with the invariants associated with this frame field. Then, we obtain a complete classification theorem for class~$\mathcal A$ surfaces. Finally, we consider some applications of this theorem.

math.DG↗
arXiv2025

Almost Ricci Solitons on Class $\mathcal A$ Hypersurfaces of Product Spaces

In this paper, we study hypersurfaces in the product spaces $\mathbb{Q}_ε^3 \times \mathbb{R}$ for which the tangential component $T$ of the vector field $\frac{\partial}{\partial t}$ is a principal direction, where $\mathbb{Q}_ε^3$ denotes the three-dimensional non-flat Riemannian space form with sectional curvature $ε= \pm 1$, and $\frac{\partial}{\partial t}$ is the unit vector field tangent to the $\mathbb{R}$-factor. We obtain a local classification of hypersurfaces with three distinct principal curvatures satisfying specific functional relations. Then, we determine the necessary and sufficient conditions for such hypersurfaces to admit an almost Ricci soliton structure with potential vector field $T$. Finally, we prove that the only hypersurfaces admitting such solitons are rotational, by showing that the constructed examples with three distinct principal curvatures do not admit almost Ricci solitons.

math.DG↗
arXiv2025

Codimensions-Two Submanifolds Contained in the Light-like Hypercylinder $\mathcal{LC}^n\times\mathbb R$

In this paper, we investigate space-like codimension-two submanifolds of the Lorentz-Minkowski space $\mathbb{E}_1^{n+2}$ constrained to lie on the light-like hypercylinder $\mathcal{LC}^n \times \mathbb{R}$ over the light cone $\mathcal{LC}^n$. By constructing a geometrically defined global frame field on the submanifold, we analyze the geometric interpretations of the associated extrinsic invariants by providing characterizations of (pseudo-)isotropic and pseudo-umbilical submanifolds, as well as submanifolds with flat normal bundle. In particular, we obtain local classification theorems for these classes of submanifolds.

math.DG↗
arXiv2024

Surfaces in Robertson-Walker Space-Times with Positive Relative Nullity

In this article, we study space-like and time-like surfaces in a Robertson-Walker space-time,, denoted by $L^4_1(f,c)$, having positive relative nullity. First, we give the necessary and sufficient conditions for such space-like and time-like surfaces in $L^4_1(f,c)$. Then, we obtain the local classification theorems for space-like and time-like surfaces in $L^4_1(f,0)$ with positive relative nullity. Finally, we consider the space-like and time-like surfaces in $\mathbb{E}^1_1\times\mathbb{S}^3$ and $\mathbb{E}^1_1\times\mathbb{H}^3$ with positive relative nullity. These are the special spaces of $L^4_1(f,c)$ when the warping function $f$ is a constant function, with $c=1$ for $\mathbb{E}^1_1\times\mathbb{S}^3$ and $c=-1$ for $\mathbb{E}^1_1\times\mathbb{H}^3$.

math.DG↗
arXiv2024

Biconservative Surfaces in Robertson-Walker Spaces

In this paper, we mainly focus on space-like PMCV surfaces in Robertson-Walker spacetimes. First, we derive certain geometrical properties of biconservative surfaces in the Robertson-Walker space $L^n_1(f, c)$ of arbitrary dimension. Then, we get complete local classifications of such surfaces in $L^4_1(f,0)$, $L^5_1(f,0)$ and $L^5_1(1,\pm 1)$. Finally, we proved that a space-like PMCV biconservative surface in $L^n_1(f,0)$ lies on a totally geodesic submanifold with dimension $4$ or $5$.

math.DG↗
arXiv2024

On Space-like Class $\mathcal A$ Surfaces in Robertson-Walker Space Times

In this article, we consider space-like surfaces in Robertson-Walker Space times $L^4_1(f,c)$ with comoving observer field $\frac{\partial}{\partial t}$. We study some problems related to such surfaces satisfying the geometric conditions imposed on the tangential part and normal part of the unit vector field $\frac{\partial}{\partial t}$ naturally defined. First, we investigate space-like surfaces in $L^4_1(f,c)$ satisfying that the tangent component of $\frac{\partial}{\partial t}$ is an eigenvector of all shape operators, called class $\mathcal A$ surfaces. Then, we get a classification theorem of space-like class $\mathcal A$ surfaces in $L^4_1(f,0)$. Also, we examine minimal space-like class $\mathcal A$ surfaces in $L^4_1(f,0)$. Finally, we give the parametrizations of space-like surfaces in $L^4_1(f,0)$ when the normal part of the unit vector field $\frac{\partial}{\partial t}$ is parallel.

math.DG↗
arXiv2024

Some Classifications for Gauss Map of Tubular Hypersurfaces in $\mathbb{E}^{4}_{1}$ Concerning Linearized Operators $\mathcal{L}_{k}$

In this study, we deal with the Gauss map of tubular hypersurfaces in 4-dimensional Lorentz-Minkowski space concerning the linearized operators $\mathcal{L}_{1}$ (Cheng-Yau) and $\mathcal{L}_{2}$. We obtain the $\mathcal{L}_{1}$ (Cheng-Yau) operator of the Gauss map of tubular hypersurfaces that are formed as the envelope of a family of pseudo hyperspheres {or pseudo hyperbolic hyperspheres} whose centers lie on timelike or spacelike curves with non-null Frenet vectors in $\mathbb{E}^{4}_{1}$ and give some classifications for these hypersurfaces which have generalized $\mathcal{L}_{k}$ 1-type Gauss map, first kind $\mathcal{L}_{k}$-pointwise 1-type Gauss map, second kind $\mathcal{L}_{k}$-pointwise 1-type Gauss map and $\mathcal{L}_{k}$-harmonic Gauss map, $k\in\{1,2\}$.

math.DG↗
arXiv2024

Rotational hypersurfaces family satisfying $\mathbb{L}_{n-3}\mathcal{G}=\mathcal{A}\mathcal{G}$ in ${\mathbb{E}}^{n}$

In this paper, we investigate rotational hypersurfaces family in $n$ -dimensional Euclidean space ${\mathbb{E}}^{n}$. Our focus is on studying the Gauss map $\mathcal{G}$ of this family with respect to the operator $\mathbb{L}_{k}$, which acts on functions defined on the hypersurfaces. The operator $\mathbb{L}_{k}$ can be viewed as a modified Laplacian and is known by various names, including the Cheng--Yau operator in certain cases. Specifically, we focus on the scenario where $k=n-3$ and $n\geq 3$. By applying the operator $\mathbb{L}_{n-3}$ to the Gauss map $\mathcal{G}$, we establish a classification theorem. This theorem establishes a connection between the $n\times n$ matrix $\mathcal{A}$, and the Gauss map $\mathcal{G}$ through the equation $\mathbb{L}_{n-3}\mathcal{G}=\mathcal{A}\mathcal{G}$.

math.DG↗
arXiv2024

Rotational hypersufaces in $E^4_1$ with generalized $L_k$ 1-type Gauss map

In this paper, we study the Gauss map of rotational hypersurfaces in 4-dimensional Lorentz-Minkowski space concerning the linear second order differential operators $L_1$ and $L_2$, where $L_1$ is usually called as the Cheng-Yau operator. We obtain some classifications of rotational hypersurfaces which have $L_k$-harmonic Gauss map, $L_k$-pointwise 1-type Gauss map and generalized $L_k$ 1-type Gauss map, where $k = 1,2$.

math.GM↗
arXiv2022

Biconservative surfaces in the $4$-dimensional Euclidean sphere

In this paper, we study biconservative surfaces with parallel normalized mean curvature vector field ($PNMC$) in the $4$-dimensional unit Euclidean sphere $\mathbb{S}^4$. First, we study the existence and uniqueness of such surfaces. We obtain that there exists a $2$-parameter family of non-isometric abstract surfaces that admit a (unique) $PNMC$ biconservative immersion in $\mathbb{S}^4$. Then, we obtain the local parametrization of these surfaces in the $5$-dimensional Euclidean space $\mathbb{E}^5$.

math.DG↗
arXiv2019

Biconservative quasi-minimal immersions into semi-Euclidean spaces

In this paper we study biconservative immersions into the semi-Riemannian space form $R^4_2(c)$ of dimension 4, index 2 and constant curvature, where $c\in\{0,-1,1\}$. First, we obtain a characterization of quasi-minimal proper biconservative immersions into $R^4_2(c)$. Then we obtain the complete classification of quasi-minimal biconservative surfaces in $R^4_2(0)=\mathbb E^4_2$. We also obtain a new class of biharmonic quasi-minimal isometric immersion into $\mathbb E^4_2$.

math.GM↗
arXiv2018

On space-like generalized constant ratio hypersufaces in Minkowski spaces

A hypersurface in a Euclidean space $\mathbb{E}^{n+1}$ is said to be a generalized constant ratio (GCR) hypersurface if the tangential part of its position vector is one of its principle directions. In this work, we move the study of generalized constant ratio hypersurfaces started in \cite% {YuFu2014GCRS} into the Minkowski space. First, we get some geometrical properties of non-degenerated GCR hypersurfaces in an arbitrary dimensional Minkowski space. Then, we obtain complete classification of GCR surfaces in the Minkowski 3-space. We also give some explicit examples.

math.DG↗
arXiv2017

On biconservative surfaces in Euclidean spaces

In this paper, we study biconservative surfaces with parallel normalized mean curvature vector in $\mathbb{E}^4$. We obtain complete local classification in $\mathbb{E}^4$ for a biconservative PNMCV surface. We also give an example to show the existence of PNMCV biconservative surfaces in $\mathbb{E}^4$.

math.DG↗