We argue that G_2 manifolds for M-theory admitting string theory Calabi-Yau duals are fibered by coassociative submanifolds. Dual theories are constructed using the moduli space of M-five-brane fibers as target space. Mirror symmetry and various string and M-theory dualities involving G_2 manifolds may be incorporated into this framework. To give some examples, we construct two non-compact manifolds with G_2 structures: one with a K3 fibration, and one with a torus fibration and a metric of G_2 holonomy. Kaluza-Klein reduction of the latter solution gives abelian BPS monopoles in 3 + 1 dimensions.
GUKOV, SERGEI; YAU, SHING-TUNG; and ZASLOW, ERIC (2003) "Duality and Fibrations on G_2 Manifolds," Turkish Journal of Mathematics: Vol. 27: No. 1, Article 4. Available at: https://journals.tubitak.gov.tr/math/vol27/iss1/4