Crossover scaling from classical to non-classical critical behaviour

Interacting physical systems in the neighborhood of criticality (and massiv e continuum field theories) can often be characterized by just two physical scales: a (macroscopic) correlation length and a (microscopic) interaction range, related to the coupling and measured by the Ginzburg number G. A cr itical crossover limit can be defined when both scales become large while t heir ratio stays finite. The corresponding scaling functions are universal, and they are related to the standard field-theory renormalization-group fu nctions. The critical crossover describes the unique flow from the Gaussian to the nonclassical fixed point.