FINITE-SIZE CORRECTIONS TO THE CORRELATION-FUNCTION OF THE SPHERICAL MODEL AT D-GREATER-THAN-OR-EQUAL-TO-4

Finite-size effects in the correlation function G(R,T;L)=[Phi(0).Phi(R )] of a spherical-model ferromagnet, confined to geometry L(d-d')X inf inity(d') (d greater than or equal to 4, d'less than or equal to 2) an d subjected to twisted boundary conditions, are analyzed. Focusing att ention on the region of first-order phase transition (T<T-c), we exami ne the influence of the twist parameter tau on the function G(R, T;L) in different regimes of the distance parameter epsilon(= R/L). Two com plementary methodologies are employed: (i) dimensional regularization involving the limit d-->4 as approached from the mean-field regime at short separations epsilon much less than 1, and (ii) zeta-function reg ularization at comparably larger separations epsilon=O(1) using genera tors from more simplified classes of sums so as to properly handle the singular features of the correlation function at d=4. Results followi ng from the two methodologies are found to be completely consistent wi th one another.