  We study open spin chains for strings stretched between giant graviton states
in the N=4 SYM field theory in the collective coordinate approach. We study the
boundary conditions and the effective Hamiltonian of the corresponding spin
chain to two loop order.
  The ground states of the spin chain have energies that match the relativistic
dispersion relation characteristic of massive W boson particles on the
worldvolume of the giant graviton configurations, up to second order in the
limit where the momentum is much larger than the mass. We find evidence for a
non-renormalization theorem for the ground state wave function of this spin
chain system. We also conjecture a generalization of this result to all loop
orders which makes it compatible with a fully relativistic dispersion relation.
We show that the conjecture follows if one assumes that the spin chain admits a
central charge extension that is sourced by the giant gravitons, generalizing
the giant magnon dispersion relation for closed string excitations. This
provides evidence for ten dimensional local physics mixing AdS directions and
the five-sphere emerging from an N=4 SYM computation in the presence of a
non-trivial background (made of D-branes) that break the conformal field theory
of the system.
