Description
Identifying which boundary conditions preserve integrability in two-dimensional sigma-models is a basic structural question, relevant from open string dynamics to impurity problems. I will discuss a simple approach that determines integrable boundary conditions through the divisor structure of the Lax connection, giving a generalisation of previous constructions. As an application, I will treat open strings on AdS3 x S3 with mixed NSNS-RR flux, where the standard approaches cease to work at generic flux, and show how the background supports integrable D-branes that wrap twisted conjugacy classes in SL(2,R)xSU(2). If time permits I will discuss this example and construction from the point of view of 4d Chern-Simons theory.