About common physical nature of divergence and interference
  The difference of actions between nearly lying unstable ``8'' and ``0'' like trajectories in two dimensions is computed by methods of chaotic dynamics. We found it to be equal to $pY\Theta/2$, where $\Theta$ is angle between paths at cross, $Y$ is distance between paths, and $p$ is momentum. This kind of periodic trajectories contributes $\tau^2$ (interference) term to spectral form-factor. 
Daniel L. Miller