-Manifolds With Parallel Characteristic Torsion
arXiv:math/0604441
Abstract
We classify 7-dimensional cocalibrated $\G_2$-manifolds with parallel characteristic torsion and non-abelian holonomy. All these spaces admit a metric connection with totally skew-symmetric torsion and a spinor field solving the equations in the common sector of type II superstring theory. There exist $\G_2$-structures with parallel characteristic torsion that are not naturally reductive.
19 pages