The higher-dimensional objects in string theory known as D-branes have been a
source of much of the interesting developements in the subject during the past
ten years. A very interesting phenomenon occurs when several of these D-branes
become coincident: The abelian gauge theory living on each brane is enhanced to
a non-abelian gauge theory living on the stack of coincident branes. This gives
rise to interesting effects like the natural appearance of non-commutative
geometry. The theory governing the dynamics of these coincident branes is still
poorly understood however. I will describe an attempt to better the situation by
using so-called boundary fermions, originating in considerations of open strings
ending on the stack of branes, and writing down actions for coincident branes
using these instead of matrices to describe the non-abelian fields. It can be
shown that by gauge-fixing and suitably quantizing these boundary fermions the
non-abelian action that is known, the Myers action, can be reproduced.
Furthermore the action formulated using boundary fermions also posseses a
symmetry known as kappa-symmetry, making it a candidate for a full
supersymmetric action for coincident D-branes, at least in a certain
approximation.
