For (3+1)-dimensional fermions, a net axial charge and external magnetic
field can lead to a current parallel to the magnetic field. This is the chiral
magnetic effect. We use gauge-gravity duality to study the chiral magnetic
effect in large-Nc, strongly-coupled N=4 supersymmetric SU(Nc) Yang-Mills
theory coupled to a number Nf << Nc of N=2 hypermultiplets in the Nc
representation of SU(Nc), i.e. flavor fields. Specifically, we introduce an
external magnetic field and a time-dependent phase for the mass of the flavor
fields, which is equivalent to an axial chemical potential for the flavor
fermions, and we compute holographically the resulting chiral magnetic current.
For massless flavors we find that the current takes the value determined by the
axial anomaly. For massive flavors the current appears only in the presence of
a condensate of pseudo-scalar mesons, and has a smaller value than for massless
flavors, dropping to zero for sufficiently large mass or magnetic field. The
axial symmetry in our system is part of the R-symmetry, and the states we study
involve a net flow of axial charge to the adjoint sector from an external
source coupled to the flavors. We compute the time rate of change of axial
charge and of energy both in field theory and from holography, with perfect
agreement. In contrast to previous holographic models of the chiral magnetic
effect, in our system the vector current is conserved and gauge-invariant
without any special counterterms.Comment: 54 pages, 18 eps files in 6 figure