Codimension-three bundle singularities in F-theory

We study new nonperturbative phenomena in N = 1 heterotic string vacua corresponding to pointlike bundle singularities in codimension three. These degenerations result in new four-dimensional infrared physics characterized by light solitonic states whose origin is explained in the dual F-theory model. We also show that such phenomena appear generically in E7→E6 higgsing and describe in detail the corresponding bundle transition.