Anomaly Inflow on Orientifold Planes

We examine some six-dimensional orientifold models with $N = 1$ supersymmetry, which can be realised as intersecting 7-branes and 7-planes. These models are studied in the light of recent work showing that orientifold planes carry anomalous gravitational couplings on their world-volume. We show that gravitational anomalies can be locally cancelled by these new couplings at every point in the internal space, under the assumption that the anomaly residing on orientifold planes is distributed in a particular way among brane-plane and plane-plane intersections.