Quantum renormalization of high-energy excitations in the 2D Heisenberg model

Abstract
We find using Monte Carlo simulations of the spin-1/2 2D square lattice nearest neighbour quantum Heisenberg antiferromagnet that the high-energy peak locations at (π, 0) and (π/2, π/2) differ by about 6%, (π/2, π/2) being the highest. This is a deviation from linear spin wave theory which predicts equal magnon energies at these points.