  We propose a perturbative asymptotic Bethe ansatz (PABA) for open spin-chain
systems whose Hamiltonians are given by matrices of anomalous dimension for
composite operators, and apply it to two types of composite operators related
to two different brane configurations. One is an AdS_4 \times S^2-brane in the
bulk AdS_5 \times S^5 which gives rise to a defect conformal field theory
(dCFT) in the dual field theory, and the other is a giant graviton system with
an open string excitation. In both cases, excitations on open strings attaching
to D-branes (a D5-brane for the dCFT case, and a spherical D3-brane for the
giant graviton case) can be represented by magnon states in the spin-chains
with appropriate boundary conditions, in which informations of the D-branes are
encoded. We concentrate on single-magnon problems, and explain how to calculate
boundary S-matrices via the PABA technique. We also discuss the energy spectrum
in the BMN limit.

High Energy Physics - Theory