Heterotic T-fects, 6D SCFTs, and F-theory

We study the (1, 0) six-dimensional SCFTs living on defects of non-geometric heterotic backgrounds (T-fects) preserving a E-7 x E-8 subgroup of E-8 x E-8. These configurations can be dualized explicitly to F-theory on elliptic K3-fibered non-compact Calabi-Yau threefolds. We find that the majority of the resulting dual threefolds contain non-resolvable singularities. In those cases in which we can resolve the singularities we explicitly determine the SCFTs living on the defect. We find a form of duality in which distinct defects are described by the same IR fixed point. For instance, we find that a subclass of non-geometric defects are described by the SCFT arising from small heterotic instantons on ADE singularities.