arXiv subjects

Dimitar Razpopov

Publications and source records attributed to Dimitar Razpopov.

12 recordsLinked to original sources

arXiv2023

Spheres and circles with respect to an indefinite metric on a Riemanian manifold with a skew-circulant structure

We study hyper-spheres, spheres and circles, with respect to an indefinite metric, in a tangent space on a 4-dimensional differentiable manifold. The manifold is equipped with a positive definite metric and an additional tensor structure of type (1, 1)11. The fourth power of the additional structure is minus identity and its components form a skew-circulant matrix in some local coordinate system. The both structures are compatible and they determine an associated indefinite metric on the manifold.

math.DG↗

arXiv2020

A Riemannian manifold with skew-circulant structures and an associated locally conformal Kähler manifold

A 4-dimensional Riemannian manifold M, equipped with an additional tensor structure S, whose fourth power is minus identity, is considered. The structure S has a skew-circulant matrix with respect to some basis of the tangent space at a point on M. Moreover, S acts as an isometry with respect to the metric g. A fundamental tensor is defined on such a manifold (M,g,S) by g and by the covariant derivative of S. This tensor satisfies a characteristic identity which is invariant to the usual conformal transformation. Some curvature properties of (M,g,S) are obtained. A Lie group as a manifold of the considered type is constructed. A Hermitian manifold associated with (M,g,S) is also considered. It turns out that it is a locally conformal Kähler manifold.

math.DG↗

arXiv2020

The value of the work done by an isotropic vector force field along an isotropic curve

In the present paper we consider a 3-dimensional differentiable manifold $M$ equipped with a Riemannian metric $g$ and an endomorphism $Q$, whose third power is the identity and $Q$ acts as an isometry on $g$. Both structures $g$ and $Q$ determine an associated metric $f$ on $(M, g, Q)$. The metric $f$ is necessary indefinite and it defines isotropic vectors in the tangent space $T_{p}M$ at an arbitrary point $p$ on $M$. The physical forces are represented by vector fields. We investigate physical forces whose vectors are in $T_{p}M$ on $(M, g, Q)$. Moreover, these vectors are isotropic and they act along isotropic curves. We study the physical work done by such forces.

math.DG↗

arXiv2018

Two types of Lie Groups as 4-dimensional Riemannian manifolds with circulant structure

A 4-dimensional Riemannian manifold equipped with an endomorphism of the tangent bundle, whose fourth power is the identity, is considered. The matrix of this structure in some basis is circulant and the structure acts as an isometry with respect to the metric. Such manifolds are constructed on 4-dimensional real Lie groups with Lie algebras of two remarkable types. Some of their geometric characteristics are obtained.

math.DG↗

arXiv2017

Three-dimensional Riemannian manifolds with circulant structures

We consider a 3-dimensional Riemannian manifold M with two circulant structures -- a metric g and an endomorphism q whose third power is identity. The structure q is compatible with g such that an isometry is induced in any tangent space of M. We obtain some curvature properties of this manifold (M, g, q) and give an explicit example of such a manifold.

math.DG↗

arXiv2017

On a Three Dimensional Riemannian Manifold with an Additional Structure

We consider a 3-dimensional Riemannian manifold with additional structure q. We find a condition that the affine structure q is parallel with respect to the Riamannian connection.We prove the sectional curvatures of three 2-sections formed linearly independent vectors are equal among them.

math.DG↗

arXiv2017

Riemannian almost product manifolds generated by a circulant structure

A 4-dimensional Riemannian manifold equipped with a circulant structure, which is an isometry with respect to the metric and its fourth power is the identity, is considered. The almost product manifold associated with the considered manifold is studied. The relation between the covariant derivatives of the almost product structure and the circulant structure is obtained. The conditions for the covariant derivative of the circulant structure, which imply that an almost product manifold belongs to each of the basic classes of the Staikova-Gribachev classification, are given.

math.DG↗

arXiv2014

Four-dimensional Riemannian manifolds with two circulant structures

We consider a class (M, g, q) of four-dimensional Riemannian manifolds M, where besides the metric g there is an additional structure q, whose fourth power is the unit matrix. We use the existence of a local coordinate system such that there the coordinates of g and q are circulant matrices. In this system q has constant coordinates and q is an isometry with respect to g. By the special identity for the curvature tensor R generated by the Riemannian connection of g we define a subclass of (M, g, q). For any (M, g, q) in this subclass we get some assertions for the sectional curvatures of two-planes. We get the necessary and sufficient condition for g such that q is parallel with respect to the Riemannian connection of g.

math.DG↗

arXiv2011

On the geometry of four dimensional Riemannian manifold with a circulant metric and a circulant affinor structure

We consider a four dimensional Riemannian manifold M with a metric g and an affinor structure q. We note the local coordinates of g and q are circulant matrices. Their first orders are (A, B, C, B), A, B, C \in FM and (0, 1, 0, 0), respectively. Let \nabla be the connection of g. Further, let mu_{1}, mu_{2},mu_{3}, mu_{4}, mu_{5}, mu_{6} be the sectional curvatures of 2-sections {x, qx}, {x, q^{2}x}, {q^{3}x, x}, {qx, q^{2}x}, {qx, q^{3}x}, {q^{2}x, q^{3}x} for arbitrary vector x in T_{p}M$, p is in M . Then we have that q^{4}=E; g(qx, qy)=g(x,y), x, y are in chiM. The main results of the present paper are 1) There exist a q-base in T_{p}M, p is in M. 2) if \nabla q=0, then μ_{1}= μ_{3}=μ_{4}=μ_{6}, μ_{2}= μ_{5}=0.

math.DG↗

arXiv2011

On a Class of Special Riemannian Manifolds

We consider a four dimensional Riemannian manifold M with a metric g and an affinor structure q. We note the local coordinates of g and q are circulant matrices. Their first orders are (A, B, C, B)(A, B, C are smooth functions on M) and (0, 1, 0, 0), respectively. Let nabla be the connection of g. Then we obtain: 1) q^{4}=id; g(qx, qy)=g(x,y), x, y are arbitrary vector fields on M, 2) nabla q =0 if and only if grad A=(grad C)q^{2}; 2.grad B= (grad C)(q+q^{3}),

math.DG↗

arXiv2010

On affine connections in a Riemannian manifold with a circulant metric and two circulant affinor structures

In the present paper it is considered a class V of 3-dimensional Riemannian manifolds M with a metric g and two affinor tensors q and S. It is defined another metric \bar{g} in M. The local coordinates of all these tensors are circulant matrices. It is found: 1)\ a relation between curvature tensors R and \bar{R} of g and \bar{g}, respectively; 2)\ an identity of the curvature tensor R of g in the case when the curvature tensor \bar{R} vanishes; 3)\ a relation between the sectional curvature of a 2-section of the type \{x, qx\} and the scalar curvature of M.

math.DG↗

arXiv2010

Almost conformal transformation in a class of Riemannian manifolds

We consider a 3-dimensional Riemannian manifold V with a metric g and an affinor structure q. The local coordinates of these tensors are circulant matrices. In V we define an almost conformal transformation. Using that definition we construct an infinite series of circulant metrics which are successively almost conformaly related. In this case we get some properties.

math.DG↗