The subject of investigations are the almost hypercomplex manifolds with Hermitian and anti-Hermitian (Norden) metrics. A linear connection D is introduced such that the structure of these manifolds is parallel with respect to D and its torsion is totally skewsymmetric. The class of the nearly Kähler manifolds with respect to the first almost complex structure is of special interest. It is proved that D has a D-parallel torsion and is weak if it is not flat. Some curvature properties of these manifolds are studied. Int. J. Geom. Methods Mod. Phys. 2011.08:115-131. Downloaded from www.worldscientific.com by UNIVERSITY OF AUCKLAND LIBRARY -SERIALS UNIT on 03/11/15. For personal use only.
The almost (H, G)-manifoldsLet (M, H) be an almost hypercomplex manifold, i.e. M is a 4n-dimensional differentiable manifold and H = (J 1 , J 2 , J 3 ) is a triple of almost complex structures with the properties:for all cyclic permutations (α, β, γ) of (1, 2, 3) and I denotes the identity ([6, 1]). The standard structure of H on a 4n-dimensional vector space with a basis {X 4k+1 , X 4k+2 , X 4k+3 , X 4k+4 } k=0,1,...,n−1 has the form [37]:Further, x, y, z, w will stand for arbitrary differentiable vector fields on M . Let g be a pseudo-Riemannian metric on (M, H) with the properties