Rolling among G₂ vacua

We consider topology-changing transitions between 7-manifolds of holonomy G₂ constructed as a quotient of CY × S¹ by an antiholomorphic involution. We classify involutions for Complete Intersection CY threefolds, focussing primarily on cases without fixed points. The ordinary conifold transition between CY threefolds descends to a transition between G₂ manifolds, corresponding in the N = 1 effective theory incorporating the light black hole states either to a change of branch in the scalar potential or to a Higgs mechanism. A simple example of conifold transition with a fixed nodal point is also discussed. As a spin-off, we obtain examples of G₂ manifolds with the same value for the sum of Betti numbers b₂ + b₃, and hence potential candidates for mirror manifolds.