Localized modes at a D-brane–O-plane intersection and heterotic Alice strings

We study a system of Nc D3-branes intersecting D7-branes and O7-planes in 1 + 1-dimensions. We use anomaly cancellation and string dualities to argue that there must be chiral fermion zero-modes on the D3-branes which are localized near the O7planes. Away from the orientifold limit we verify this by using index theory as well as explicit construction of the zero-modes. This system is related to F-theory on K3 and heterotic matrix string theory, and the heterotic strings are related to Alice string defects in N = 4 Super-Yang-Mills. In the limit of large Nc we find an AdS3 dual of the heterotic matrix string CFT.