The First Three Yoctoseconds of Relativistic Heavy-Ion Collisions

The recent results of the hydrodynamic calculations describing consistently one- and two-particle observables in relativistic heavy-ion collisions suggest that interesting phenomena may take place at the very early stages of the collisions. Firstly, the successful hydrodynamic fits indicate that the initial conditions for the hydrodynamic equations may differ from those obtained from the Glauber model. This may hint to yet unrecognized mechanisms of the particle production and thermalization which are responsible for such modified initial conditions. Secondly, the thermalization processes may be preceded by the free-streaming stage. It is also plausible, that the full three-dimensional hydrodynamic expansion is preceded by the purely transverse, two-dimensional hydrodynamic evolution. Such observations emphasize the importance of the proper matching between the microscopic models of early stages and the hydrodynamic evolution. In this respect, physics of the first 1 fm/c or, equivalently, of the first three yoctoseconds becomes an exciting subject of present and future investigations. (authors)