A Spin(7) Conifold Transition in Type IIB as an F-theory Flop

We consider type IIB string theory compactified on an 8-dimensional Spin(7) manifold with N D5-branes, undergoing a conifold transition to a geometry with no branes and N units of dual 3-form RR flux through appropriate 3-cycles. We show that at constant IIB coupling, in the limit of large N and finite ’t Hooft coupling, this conifold transition can be lifted to a purely geometric S flop in the 11-dimensional space of an equivalent F-theory without branes and fluxes. The S flop in this equivalent F-theory is a higher-dimensional analogue of the S flop in M-theory on a G2 manifold discovered by Atiyah et al., albeit resulting in a theory with N = 1 in d = 2 instead of d = 4. ∗E-mail: [email protected]