The Tower of States and the Entanglement Spectrum in a Coplanar Antiferromagnet

We extend the analytical arguments of Metlitski and Grover (arXiv:1112.5166) to compute the entanglement spectrum and entanglement entropy of coplanar antiferromagnets with $SO(3)$ order parameter symmetry. The low-energy states in the entanglement spectrum exhibit the tower of states structure, as is expected for systems that undergo spontaneous symmetry breaking. Our results are consistent with numerical results on the triangular and Kagom\'{e} lattice.