Universal amplitude ratios in the Ising model in three dimensions

We use a high-precision Monte Carlo simulation to determine the universal specific-heat amplitude ratio A(+)/A(-) in the three-dimensional Ising model via the impact angle phi of complex temperature zeros. We also measure the correlation-length critical exponent nu from finite-size scaling and the specific-heat exponent a through hyperscaling. Extrapolations to the thermodynamic limit yield phi = 59.2(1.0)degrees, A(+)/A(-) = 0.56(3), nu = 0.630 48(32) and alpha = 0.1086(10). These results are compatible with some previous estimates from a variety of sources and rule out recently conjectured exact values.