Anomalous chirality fluctuations in the initial stage of heavy ion collisions and parity odd bubbles

We compute numerically the topological charge distribution in the initial stage of a high energy heavy ion collision. This charge distribution is generated by Chern–Simons number fluctuations associated with the dynamics of strong classical fields in the initial state. The distribution is found to be quite narrow at RHIC and LHC energies; we argue that this is a consequence of the strict boost invariance of the initial field configurations. A substantial generation of topological charge, as required in the P-odd bubble scenario [D. Kharzeev, et al., Phys. Rev. Lett. 81 (1998) 512], can only occur if strict boost invariance is lost in the later stages of the collision. This could be naturally achieved if the system approaches thermalization.