  In the chiral magnetic effect, there is a competition between a strong
magnetic field, which tends to project positively charged particles to have
spin aligned along the magnetic field, and a chirality imbalance which may be
produced locally by a topologically nontrivial gauge field such as an
instanton. We study the properties of the Euclidean Dirac equation for a light
fermion in the presence of both a constant abelian magnetic field and an SU(2)
instanton. In particular, we analyze the zero modes analytically in various
limits, both on R^4 and on the four-torus, in order to compare with recent
lattice QCD results, and study the implications for the electric dipole moment.
