Spinc-quantization and the K-multiplicities of the discrete series
This paper deals with Dirac, twistor and Killing equations on Weyl manifolds with -spin structures. A conformal Schrödinger-Lichnerowicz formula is presented and used to derive integrability conditions for these equations. It is shown that the only non-closed Weyl manifolds of dimension greater than 3 that admit solutions of the real Killing equation are 4-dimensional and non-compact. Any Weyl manifold of dimension greater than 3, that admits a real Killing spinor has to be Einstein-Weyl.
In his famous five variables paper Elie Cartan showed that one can canonically associate to a generic rank 2 distribution on a 5 dimensional manifold a Cartan geometry modeled on the homogeneous space , where is one of the maximal parabolic subgroups of the exceptional Lie group . In this article, we use the algebra of split octonions to give an explicit global description of the distribution corresponding to the homogeneous model.
P. Bérard et D. Meyer ont démontré une inégalité du type Faber-Krahn pour les domaines d'une variété compacte à courbure de Ricci positive. Nous démontrons des résultats de stabilité associés à cette inégalité.
Nous caractérisons les couples de fonctions différentiables , définies sur une variété compacte de dimension , qui sont simultanément stables en ce sens que, pour tout couple assez voisin, il existe un difféomorphisme de et deux difféomorphismes et de tels que et échangent et alors que et échangent et . L’outil essentiel est une technique de résolution des équations du type où les inconnues et sont des fonctions de classe .
In this paper, we define an -Yang-Mills functional, and hence -Yang-Mills fields. The first and the second variational formulas are calculated, and the stabilities of -Yang-Mills fields on some submanifolds of the Euclidean spaces and the spheres are investigated, and hence the theories of Yang-Mills fields are generalized in this paper.
A new concept of stability, closely related to that of structural stability, is introduced and applied to the study of C¹ endomorphisms with singularities. A map that is stable in this sense is conjugate to each perturbation that is equivalent to it in a geometric sense. It is shown that this kind of stability implies Axiom A and Ω-stability, and that every critical point is wandering. A partial converse is also shown, providing new examples of C³ structurally stable maps.
We introduce a higher dimensional analogue of the Engel structure, motivated by the Cartan prolongation of contact manifolds. We study the stability of such structure, generalizing the Gray-type stability results for Engel manifolds. We also derive local normal forms defining such a distribution.