M-theory conifolds

Seven manifolds of G2 holonomy provide a bridge between M-theory and string theory, via Kaluza-Klein reduction to Calabi-Yau six manifolds. We find first-order equations for a new family of G2 metrics D7, with S3 x S3 principal orbits. These are related at weak string coupling to the resolved conifold, paralleling earlier examples B7 that are related to the deformed conifold, allowing a deeper study of topology change and mirror symmetry in M-theory. The D7 metrics' nontrivial parameter characterizes the squashing of an S3 bolt, which limits to S2 at weak coupling. In general the D7 metrics are asymptotically locally conical, with a nowhere-singular circle action.