Large-N estimates of universal amplitudes of the CPN-1 theory and comparison with a S=1/2 square-lattice model with competing four-spin interactions

We present computations of certain finite-size scaling functions and universal amplitude ratios in the large-N limit of the CPN-1 field theory. We pay particular attention to the uniform susceptibility, the spin stiffness, and the specific heat. Field theoretic arguments have shown that the long-wavelength description of the phase transition between the Neel and valence-bond solid states in square lattice S = 1/2 antiferromagnets is expected to be the noncompact CP1 field theory. We provide a detailed comparison between our field theoretic calculations and quantum Monte Carlo data close to the Neel-VBS transition on a S = 1/2 square-lattice model with competing four-spin interactions (the JQ model).