Quantum caustics and the hierarchy of light cones in quenched spin chains

We show that the light conelike structures that form in spin chains after a quench are quantum caustics. Their natural description is in terms of catastrophe theory and this implies (1) a hierarchy of light cone structures corresponding to the different catastrophes, (2) dressing by characteristic wave functions that obey scaling laws determined by the Arnol'd and Berry indices, and (3) a network of vortex-antivortex pairs in space-time inside …