Explain the mechanism that decouples apsidal corotation

Identify the dynamical mechanism responsible for the decoupling of apsidal corotation and the consequent loss of coherent apsidal precession in highly eccentric, initially apsidally aligned planetary systems.

Background

The simulations show that instability in initially aligned systems is preceded by a non-periodic growth in the amplitude of relative apsidal-angle oscillations. A planetary pair then loses synchronized precession, develops differential precession, and can undergo orbit intersection and collision. Once precession decouples, the relative eccentricities increase and mean-motion resonances broaden, potentially producing resonance overlap and chaotic evolution.

Although the observed sequence of events is described, the physical process that causes coherent apsidal precession to fail is not established.