Entanglement of magnon excitations in spin chains

We calculate exactly the entanglement content of magnon excited states in integrable spin-1/2 XXX and XXZ chains scaling limit. In particular, we show that as far number magnons with respect to size system is small one can decompose content, limit, sum particular free fermionic or bosonic theories. addition conjecture generic translational invariant Hamiltonians be also classified, operator Hamiltonian certain circumstances. Our results effectively classify wide range spin