
Journal of Lie Theory 26 (2016), No. 1, 011048 Copyright Heldermann Verlag 2016 Invariant Connections with SkewTorsion and ∇Einstein Manifolds Ioannis Chrysikos Department of Mathematics and Statistics, Masaryk University, Brno 611 37, Czech Republic chrysikosi@math.muni.cz [Abstractpdf] \def\g{{\frak g}} For a compact connected Lie group $G$ we study the class of biinvariant affine connections whose geodesics through $e\in G$ are the 1parameter subgroups. We show that the biinvariant affine connections which induce derivations on the corresponding Lie algebra $\g$ coincide with the biinvariant metric connections. Next we describe the geometry of a naturally reductive space $(M=G/K,g)$ endowed with a family of $G$invariant connections $\nabla^{\alpha}$ whose torsion is a multiple of the torsion of the canonical connection $\nabla^{c}$. For the spheres S$^6$ and S$^7$ we prove that the space of G$_2$ (respectively, Spin(7))invariant affine or metric connections consists of the family $\nabla^{\alpha}$. We examine the ``constancy'' of the induced Ricci tensor Ric$^{\alpha}$ and prove that any compact isotropy irreducible standard homogeneous Riemannian manifold, which is not a symmetric space of Type I, is a $\nabla^{\alpha}$Einstein manifold for any $\alpha\in\mathbb{R}$. We also provide examples of $\nabla^{\pm 1}$Einstein structures for a class of compact homogeneous spaces $M=G/K$ with two isotropy summands. Keywords: Invariant connection with skewsymmetric torsion, naturally reductive space, Killing metric, nablaEinstein structure. MSC: 53C025, 53C30, 22E46 [ Fulltextpdf (573 KB)] for subscribers only. 