  Aharony, Bergman, Jafferis, and Maldacena have proposed that the low-energy
description of multiple M2-branes at a C4/Zk singularity is a (2+1)-dimensional
N=6 supersymmetric U(Nc) x U(Nc) Chern-Simons matter theory, the ABJM theory.
In the large-Nc limit, its holographic dual is supergravity in AdS4 x S7/Zk. We
study various ways to add fields that transform in the fundamental
representation of the gauge groups, i.e. flavor fields, to the ABJM theory. We
work in a probe limit and perform analyses in both the supergravity and field
theory descriptions. In the supergravity description we find a large class of
supersymmetric embeddings of probe flavor branes. In the field theory
description, we present a general method to determine the couplings of the
flavor fields to the fields of the ABJM theory. We then study four examples in
detail: codimension-zero N=3 supersymmetric flavor, described in supergravity
by Kaluza-Klein monopoles or D6-branes; codimension-one N=(0,6) supersymmetric
chiral flavor, described by D8-branes; codimension-one N=(3,3) supersymmetric
non-chiral flavor, described by M5/D4-branes; codimension-two N=4
supersymmetric flavor, described by M2/D2-branes. Finally we discuss special
physical equivalences between brane embeddings in M-theory, and their
interpretation in the field theory description.
