Crossover scaling from classical to nonclassical critical behavior

We study the crossover between classical and nonclassical critical behavior s. The critical crossover limit is driven by the Ginzburg number G. The cor responding scaling functions are universal with respect to any possible mic roscopic mechanism which can vary G, such as changing the range or the stre ngth of the interactions. The critical crossover describes the unique flow from the unstable Gaussian to the stable nonclassical fixed point. The scal ing functions are related to the continuum renormalization-group functions. We show these features explicitly in the large-N limit of the O(N) phi(4) model. We also show that the effective susceptibility exponent is nonmonoto nic in the low-temperature phase of the three-dimensional Ising model. [S10 63-651X(98)14012-6].