Critical behavior of the three-dimensional XY universality class - art. no. 214503

We improve the theoretical estimates of the critical exponents for the thre e-dimensional XY universality class. We fine alpha=-0.0146(8), gamma =1.317 7(5), nu =0.671 55(27), eta =0.0380(4), beta =0.3485(2), and delta =4.780(2 ). We observe a discrepancy with the most recent experimental estimate of a lpha; this discrepancy calls for further theoretical and experimental inves tigations. Our results are obtained by combining Monte Carlo simulations ba sed on finite-size scaling methods, and high-temperature expansions. Two im proved models (with suppressed leading scaling corrections) are selected by Monte Carlo computation. The critical exponents are computed from high-tem perature expansions specialized to these improved models. By the same techn ique we determine the coefficients of the small-magnetization expansion of the equation of state. This expansion is extended analytically by means of approximate parametric representations, obtaining the equation of state in the whole critical region. We also determine the specific-heat amplitude ra tio.