The fluctuations of quadrangular flow
  The ATLAS Collaboration has measured for the first time the fourth cumulant of quadrangular flow, $v_4\{4\}^4$. Unlike the fourth cumulants of elliptic and triangular flows, it presents a change of sign above 30\% centrality. We show that this change of sign is predicted by event-by-event hydrodynamics. We argue that it results from the combined effects of a nonlinear hydrodynamic response, which couples quadrangular flow to elliptic flow, and elliptic flow fluctuations. 
Giuliano Giacalone, Li Yan, Jacquelyn Noronha-Hostler, Jean-Yves   Ollitrault
nucl-th hep-ph nucl-ex