“…In the compactification of heterotic string theory to four dimensional Minkowski spacetime [12,61,52], the internal six-manifolds can become non-Kähler in the presence of fluxes. Various models of constructing heterotic manifolds and their vector-bundles have been put forward, see for example [52,9,17,18,10,5,36,6,13,4]. They play an important role in searching for realistic string theory vacua with four dimensional Minkowski spacetime.…”