$$\fracdjd\ln D = - 2 j^2 + 2 j^3 + \dots$$
$$H = \sum_k,\sigma \epsilon_k c^\dagger_k\sigma c_k\sigma + J \mathbfS \cdot \mathbfs(0)$$ $$\fracdjd\ln D = - 2 j^2 + 2
For small $j>0$, $dj/d\ln D = -2j^2 < 0$ → as we lower the cutoff $D$ (i.e., lower temperature), $j$ increases . This is the opposite of asymptotic freedom in QCD; it is infrared slavery . The flow diverges at a scale $D \sim T_K$, signaling a new fixed point. $dj/d\ln D = -2j^2 <
