I-Brane Dynamics

We study the dynamics near a 1 + 1 dimensional intersection of two orthogonal stacks of fivebranes in type IIB string theory, using an open string description valid at weak coupling, and a closed string description valid at strong coupling. The weak coupling description suggests that this system is invariant under eight supercharges with a particular chirality in 1 + 1 dimensions, and its spectrum contains chiral fermions localized at the intersection. The closed string description leads to a rather different picture – a three dimensional Poincare invariant theory with a gap and sixteen supercharges. We show that this dramatic change in the behavior of the system is partly due to anomaly inflow. Taking it into account leads to a coherent picture, both when the fivebranes in each stack are coincident and when they are separated.