Extremal theorems for Riemann spaces with curvature bounded above. I

Siberian Mathematical Journal -     

The spinor and tensor fields with higher spin on spaces of constant curvature

Annals of Global Analysis and Geometry - In this article, we give all the Weitzenböck-type formulas among the geometric first-order differential operators on the spinor fields with spin...     

Canonical connections with an algebraic curvature tensor field on naturally reductive spaces

We study Ambrose-Singer connections with an algebraic curvature tensor on simply connected manifolds carrying a homogeneous Riemannian structure of class ₃ in the classification given by F. Tricerri and L. Vanhecke.This work was partially supported by MURST.     

Centralisers of spaces of symmetric tensor products and applications

We show that the centraliser of the space of n-fold symmetric injective tensors, n≥2, on a real Banach space is trivial. With a geometric condition on the set of extreme points of its dual, the space of integral polynomials we obtain the same result for complex Banach spaces. We give some applications of this results to centralisers of spaces of homogeneous polynomials and complex Banach spaces. In addition, we derive a Banach-Stone Theorem for spaces of vector-valued approximable polynomials. This project was supported in part by Enterprise Ireland, International Collaboration Grant – 2004 (IC/2004/009). The second author was also partially supported by PIP 5272,UBACYTX108 and PICT 03-15033     

Almost geodesic mappings of Riemann spaces onto symmetric Riemann spaces

It is shown that if a Riemann space V_n admits a reduced almost geodesic mapping Π₂ onto a symmetric Riemann space ¯V_n, then ¯V_n has constant curvature, and V_n is itself a symmetric space.     

Divisor spaces on punctured Riemann surfaces

In this paper, we study the topology of spaces of -tuples of positive divisors on (punctured) Riemann surfaces which have no points in common (the divisor spaces). These spaces arise in connection with spaces of based holomorphic maps from Riemann surfaces to complex projective spaces. We find that there are Eilenberg-Moore type spectral sequences converging to their homology. These spectral sequences collapse at the term, and we essentially obtain complete homology calculations. We recover for instance results of F. Cohen, R. Cohen, B. Mann and J. Milgram, The topology of rational functions and divisors of surfaces, Acta Math. 166 (1991), 163-221. We also study the homotopy type of certain mapping spaces obtained as a suitable direct limit of the divisor spaces. These mapping spaces, first considered by G. Segal, were studied in a special case by F. Cohen, R. Cohen, B. Mann and J. Milgram, who conjectured that they split. In this paper, we show that the splitting does occur provided we invert the prime two.

     

Quasi-positive curvature on Bazaikin spaces

Annals of Global Analysis and Geometry - We completely characterize the sectional curvature of all of the 13-dimensional Bazaikin spaces. In particular, we show that all Bazaikin spaces admit a...     

Transformations on tensor spaces II

We prove that a linear map of one tensor product space to another sending decomposable tensors to decomposable tensors is essentially a tensor product of linear maps of products of component factors of the domain into a selection of the factors of the range. The product of those factors of the domain not involved in the above is collapsed via a linear functional, and those factors in the range left out of the above provide a common factor in the range. In the statement of the main theorem the flanking maps are induced by permutations of the factors of the domain and the range and they present the products in manageable form. It is assumed that the underlying field has at least five members, but the necessity of this assumption is not settled. All vector spaces are finite dimensional and the tensor products have finitely many components.     

Linear transformations on tensor spaces

Let U⊗V denote the tensor product of two finite dimensional vector spaces U and V over an infinite field. Let k be a positive integer such that k≤dim U and k≤ dim V Let D_k denote the set of all non-zero elements of U⊗V of rank less than k. In this paper we study linear transformations T on U⊗V such that (TD_k)⊆D_k.     

Prehomogeneous tensor spaces

We refine the classification of prehomogeneous vector spaces provided by Sato and Kimura in the case of tensor spaces, presenting a quick way to determine whether a given tensor space is prehomogeneous or not.     

Tensor invariants and homogeneous Riemann spaces

Homogeneous Riemann spaces M = $ {\mathcal p} $ /? with an irreducible isotropy group are considered. On such spaces dimensions are calculated for spaces of $ {\mathcal p} $ -invariant tensor fields of valence 2, 3, 4. In particular, consideration is given to homogeneous spaces whose isotropy groups are given by the diagrams given in Table 8.     

On integral formulas for submanifolds of spaces of constant curvature and some applications

Integral formulas of Minkowski type, involving the higher mean curvatures as multilinear forms on the normal bundle, are proved for compact oriented immersed submanifolds with arbitrary codimension in a Riemannian manifold of constant curvature, and as application a generalization of the Liebmann-Süss theorem as well as upper bounds for the first positive eigenvalue of the Laplace operator are given.