QUANTITATIVE STUDY OF THE KOSTERLITZ-THOULESS PHASE-TRANSITION IN A SYSTEM OF 2-DIMENSIONAL PLANE ROTATORS (XY MODEL) - HIGH-TEMPERATURE EXPANSIONS TO ORDER BETA(20)

High-temperature series expansions of the spin-spin correlation function for the plane rotator (or XY) model on the square lattice are extended by three terms through order beta20. Tables of the expansion coefficients are reported for the correlation function spherical moments of order l = 0, 1, 2. The expansion coefficients through beta15 for the vorticity are also tabulated. Our analysis of the series supports the Kosterlitz-Thouless predictions on the structure of the critical singularities and leads to fairly accurate estimates of the critical parameters.