Quantum Phase Transitions of Frustrated Heisenberg Antiferromagnets: a   Comprehensive Renormalization Approach
  We develop a novel renormalization approach for frustrated quantum antiferromagnets. It is designed to consistently treat spin-wave interactions all over the magnetic Brillouin zone, including high-energy modes in outer regions as well as low energy modes in the center. Focusing on the paradigmatic $J_1$-$J_2$ model, we find a unifying description of the second-order transition between the N\'eel phase and the paramagnetic phase and the first-order transition between the N\'eel phase and the columnar phase. Our approach provides explicit results for the renormalized values of the spin stiffness and spin-wave velocity characterizing the low-energy magnons in the N\'eel phase. 
Frank Kr\"uger and Stefan Scheidl