Viscosity vs. Vorticity in the Quark-Gluon Plasma

We show that, in a holographic or gauge-gravity approach to the study of the Quark-Gluon Plasma, the specific entropy density of the plasma produced in a peripheral heavy-ion collision can be strongly suppressed relative to its value for central collisions at the same impact energy; this is connected with the strong vorticity fields which are now known to characterize the peripheral case. This implies, within the holographic model, that the shear viscosity of peripheral plasmas' may be considerably lower than that of the corresponding central plasmas’, with potentially important consequences for other aspects of QGP physics, such as the centrality dependence of jet quenching.