CALCULATION OF UNIVERSAL AMPLITUDE RATIOS IN 3-LOOP ORDER

For the universality class of three-dimensional Ising systems the rati o of the high- and low-temperature amplitudes for the correlation leng th and for the susceptibility are universal quantities. They can be ca lculated by renormalized perturbation theory for scalar phi(4) theory in fixed dimensions D = 3 in the symmetric phase and in the phase of b roken symmetry. In this article the amplitude ratios are calculated in the three-loop approximation. Using the fixed point values of the cou pling constants we obtain f(+)/f(-) = 2.013(28) and C-+/C-- = 4.72(17) .