Universal amplitude ratios in the critical two-dimensional Ising model on a torus

Using results from conformal field theory, we compute several universal amplitude ratios for the two-dimensional Ising model at criticality on a symmetric torus. These include the correlation-length ratio x* = lim(L-->infinity) xi(L)/L and the first four magnetization moment ratios V(2n) = [M(2n)]/[M(2)](n). As a corollary we get the first four renormalized 2n-point coupling constants for the massless theory on a symmetric torus, G(2n)*. We confirm these predictions by a high-precision Monte Carlo simulation.