Index theorems and domain walls

The Atiyah-Patodi-Singer (APS) index theorem relates the index of a Dirac operator to an integral of the Pontryagin density in the bulk (which is equal to global chiral anomaly) and an eta invariant on the boundary (which de fines the parity anomaly). We show that the APS index theorem holds for con figurations with domain walls that are de fined as surfaces where background gauge fields have discontinuities.