Strongly coupled phases of $\mathcal{N}=1$ S-duality

Understand

We analyze S-duality of orientifolds of the Calabi-Yau cone over the first del Pezzo surface ($dP_1$).

• The S-duals of known phases, described by quiver gauge theories, contain intrinsically strongly-coupled sectors.
• These sectors are realized by a higher multiplicity intersection of NS5 branes and D5 branes atop an O5 plane, and can be thought of as stuck at the infinite coupling point between two Seiberg-dual gauge theories.
• We argue that such sectors appear generically in orientifolds of non-orbifold singularities, where in many examples every orientifold phase contains such a sector.