Spiky strings and giant magnons onS5

Recently, classical solutions for strings moving in AdS5 x S5 have played animportant role in understanding the AdS/CFT correspondence. A large set of themwere shown to follow from an ansatz that reduces the solution of the stringequations of motion to the study of a well-known integrable 1-d system known asthe Neumann-Rosochatius (NR) system. However, other simple solutions such asspiky strings or giant magnons in S5 were not included in the NR ansatz. Weshow that, when considered in the conformal gauge, these solutions can be alsoaccomodated by a version of the NR-system. This allows us to describe in detaila giant magnon solution with two additional angular momenta and show that itcan be interpreted as a superposition of two magnons moving with the samespeed. In addition, we consider the spin chain side and describe thecorresponding state as that of two bound states in the infinite SU(3) spinchain. We construct the Bethe ansatz wave function for such bound state.Comment: 33 pages, LaTeX, 2 figures. v2: minor corrections, v3: minor corrections, figures enlarge