  The effects of angular momentum conservation in peripheral heavy ion
collisions at very high energy are investigated. It is shown that the initial
angular momentum of the quark-gluon plasma should enhance the azimuthal
anisotropy of particle spectra (elliptic flow) with respect to the usual
picture where only the initial geometrical eccentricity of the nuclear overlap
region is responsible for the anisotropy. In hydrodynamical terms, the initial
angular momentum entails a non trivial dependence of the initial longitudinal
flow velocity on the transverse coordinates. This gives rise to a non-vanishing
vorticity in the equations of motion which enhances the expansion rate of the
supposedly created fluid compensating for the possible quenching effect of
viscosity. A distinctive signature of the vorticity in the plasma is the
generation of an average polarization of the emitted hadrons, for which we
provide analytical expressions. These phenomena might be better observed at
LHC, where the initial angular momentum density will be larger and where we
envisage an increase of the elliptic flow coefficient v_2 with respect to RHIC
energies.
