Universal amplitudes in the finite-size scaling of three-dimensional spin models

In a Monte Carlo study using a cluster update algorithm we investigate fini te-size scaling (FSS) of the correlation lengths of several representatives of the class of three-dimensional classical O(n) symmetric spin models on the geometry T-2 X R. For all the models we find strong evidence of a linea r relation between FSS amplitudes and scaling dimensions when applying anti periodic instead of periodic boundary conditions across the torus. This typ e of scaling relation can be proven analytically for systems on two-dimensi onal strips with periodic boundary conditions using conformal field theory.