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1.
This paper is devoted to a systematic presentation of the essential results of research on affine conformal vector fields (ACV) and to exhibit the state of art as it now stands. Of particular interest is the new information on the existence of ACVs in compact orientable semi-Riemannian manifolds, their link with first integrals of the geodesics and the separability structures.  相似文献   

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Here, it is shown that every vector field on a Finsler space which keeps geodesic circles invariant is conformal. A necessary and sufficient condition for a vector field to keep geodesic circles invariant, known as concircular vector fields, is obtained. This leads to a significant definition of concircular vector fields on a Finsler space. Finally, complete Finsler spaces admitting a special conformal vector field are classified.  相似文献   

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We acknowledge the support by the Swiss National Science Foundation  相似文献   

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We characterize the boundary value of homegeneous solutions of planar one-sided locally solvable vector fields with analytic coefficients with the property that the Lp norm of their traces is locally uniformly bounded, 0<p?1. For p≠1/n, , the boundary value must locally belong to the local Hardy space hp(R) of Goldberg while for p=1/n, , the answer calls for a new class of atomic Hardy spaces if the vector field is of infinite type at some boundary point.  相似文献   

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Let (M = G/H;g)denote a four-dimensional pseudo-Riemannian generalized symmetric space and g = m + h the corresponding decomposition of the Lie algebra g of G. We completely determine the harmonicity properties of vector fields belonging to m. In some cases, all these vector fields are critical points for the energy functional restricted to vector fields. Vector fields defining harmonic maps are also classified, and the energy of these vector fields is explicitly calculated.  相似文献   

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Summary. We study two classes of vector fields on the path space over a closed manifold with a Wiener Riemannian measure. By adopting the viewpoint of Yang-Mills field theory, we study a vector field defined by varying a metric connection. We prove that the vector field obtained in this way satisfies a Jacobi field equation which is different from that of classical one by taking in account that a Brownian motion is invariant under the orthogonal group action, so that it is a geometric vector field on the space of continuous paths, and induces a quasi-invariant solution flow on the path space. The second object of this paper is vector fields obtained by varying area. Here we follow the idea that a continuous semimartingale is indeed a rough path consisting of not only the path in the classical sense, but also its Lévy area. We prove that the vector field obtained by parallel translating a curve in the initial tangent space via a connection is just the vector field generated by translating the path along a direction in the Cameron-Martin space in the Malliavin calculus sense, and at the same time changing its Lévy area in an appropriate way. This leads to a new derivation of the integration by parts formula on the path space. Received: 8 August 1996 / In revised form: 8 January 1997  相似文献   

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In this paper we examine different aspects of the geometry of closed conformal vector fields on Riemannian manifolds. We begin by getting obstructions to the existence of closed conformal and nonparallel vector fields on complete manifolds with nonpositive Ricci curvature, thus generalizing a theorem of T.K. Pan. Then we explain why it is so difficult to find examples, other than trivial ones, of spaces having at least two closed, conformal and homothetic vector fields. We then focus on isometric immersions, firstly generalizing a theorem of J. Simons on cones with parallel mean curvature to spaces furnished with a closed, Ricci null conformal vector field; then we prove general Bernstein-type theorems for certain complete, not necessarily cmc, hypersurfaces of Riemannian manifolds furnished with closed conformal vector fields. In particular, we obtain a generalization of theorems J. Jellett and A. Barros and P. Sousa for complete cmc radial graphs over finitely punctured geodesic spheres of Riemannian space forms.  相似文献   

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We consider the vector space of continuousm-homogeneous polynomials between topological vector spaces over a non-trivially valued field of characteristic zero and certain natural vector topologies on such spaces, and we prove polynomial versions of certain well known theorems of the linear theory of locally convex spaces. Partially supported by CNPq.  相似文献   

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We investigate the deductive strength of statements concerning vector spaces over specific fields in the hierarchy of various choice principles.  相似文献   

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Motivated by the well-known Paley graphs over finite fields and their generalizations, in this paper we explore a natural multiplicative-additive analogue of such graphs arising from vector spaces over finite fields. Namely, if n2 and UFqn is an Fq-vector space, GU is the (undirected) graph with vertex set V(GU)=Fqn and edge set E(GU)={(a,b)Fqn2|ab,abU}. We describe the structure of an arbitrary maximal clique in GU and provide bounds on the clique number ω(GU) of GU. In particular, we compute the largest possible value of ω(GU) for arbitrary q and n. Moreover, we obtain the exact value of ω(GU) when UFqn is any Fq-vector space of dimension dU{1,2,n1}.  相似文献   

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In this work, it is proved that if a complete Finsler manifold of positive constant Ricci curvature admits a solution to a certain ODE, then it is homeomorphic to the n-sphere. Next, a geometric meaning is obtained for solutions of this ODE, which is applicable to Einstein–Randers spaces. Moreover, some results on Finsler spaces admitting a special conformal vector field are obtained.  相似文献   

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