  The decorrelation of the orientation of the event-plane angles in the initial
state of relativistic Pb-Pb and p-Pb collisions, the "torque effect," is
studied in a model of entropy deposition in the longitudinal direction
involving fluctuations of the longitudinal source profile on large scales. The
radiation from a single wounded nucleon is asymmetric in space-time rapidity.
It is assumed that the extent in rapidity of the region of deposited entropy is
random. Fluctuations in the deposition of entropy from each source increase the
event-plane decorrelation: for Pb-Pb collisions they improve the description of
the data, while for p-Pb collisions the mechanism is absolutely essential to
generate any sizable decorrelation. We also show that the experimental data for
rank-four flow may be explained via folding of the elliptic flow. The results
suggest the existence of long range fluctuations in the space-time distribution
of entropy in the initial stages of relativistic nuclear collisions.
