Wrapping interactions and a new source of corrections to the spin-chain/string duality

Assuming that the world-sheet sigma-model in the AdS/CFT correspondence is an integrable {\em quantum} field theory, we deduce that there might be new corrections to the spin-chain/string Bethe ansatz paradigm. These come from virtual particles propagating around the circumference of the cylinder and render Bethe ansatz quantization conditions only approximate. We determine the nature of these corrections both at weak and at strong coupling in the near BMN limit, and find that the first corrections behave qualitatively as wrapping interactions at weak coupling.