CONFORMAL ANOMALY AND CRITICAL EXPONENTS OF THE XY ISING-MODEL

We use extensive Monte Carlo transfer-matrix calculations on infinite strips of widths L up to 30 lattice spacings and a finite-size scaling analysis to obtain critical exponents and conformal anomaly number c for the two-dimensional XY Ising model. This model is expected to desc ribe the critical behavior of a class of systems with simultaneous U(1 ) and Z(2) symmetries of which the fully frustrated XY model is a spec ial case. The effective values obtained for c show a significant decre ase with L at different points along the line where the transition to the ordered phase takes place in a single transition. Extrapolations b ased on power-law corrections give values consistent with c = 3/2 alth ough larger values cannot be ruled out. Critical exponents are obtaine d more accurately and are consistent with previous Monte Carlo simulat ions suggesting nonstandard critical behavior and with recent calculat ions for the frustrated XY model.