Behavior of Two-Point Correlation Functions at High Temperatures

The asymptotic decay of the general two-point correlation function GAB(→R) at high temperatures is analyzed on the basis of the d-dimensional, spin-{} Ising model in general field H. For H≠0 the Ornstein-Zernike form ≈DADBe^-κRR^(d-1)2 is found for general ^A and ^B. However for certain operators, including the energy, the amplitude of the Ornstein-Zernike term vanishes as H² and in zero field only the higher order decay ~e^-2κRRᵈ remains. The relation to approximate treatments and to critical-point phenomena is discussed briefly.