Strong-coupling analysis of two-dimensional O(N) σ models with N≥3 on square, triangular, and honeycomb lattices

Recently generated long strong-coupling series for the two-point Green close-quote s functions of asymptotically free O(N) lattice σ models are analyzed, focusing on the evaluation of dimensionless renormalization-group-invariant ratios of physical quantities and applying resummation techniques to series in the inverse temperature β and in the energy E. Square, triangular, and honeycomb lattices are considered, as a test of universality and in order to estimate systematic errors. Large-N solutions are carefully studied in order to establish benchmarks for series coefficients and resummations. Scaling and universality are verified. All invariant ratios related to the large-distance properties of the two-point functions vary monotonically with N, departing from their large-N values only by a few per mille even down to N=3. copyright 1996 The American Physical Society