  We consider M-theory on compact spaces of G_2 holonomy constructed as
orbifolds of the form (CY x S^1)/Z_2 with fixed point set \Sigma on the CY.
This describes N=1 SU(2) gauge theories with b_1(\Sigma) chiral multiplets in
the adjoint. For b_1=0, it generalizes to compact manifolds the study of the
phase transition from the non-Abelian to the confining phase through
geometrical S^3 flops. For b_1=1, the non-Abelian and Coulomb phases are
realized, where the latter arises by desingularization of the fixed point set,
while an S^2 x S^1 flop occurs. In addition, an extremal transition between G_2
spaces can take place at conifold points of the CY moduli space where
unoriented membranes wrapped on CP^1 and RP^2 become massless.

High Energy Physics - Theory