We study the possibility that partonic matter produced at early stage of
ultrarelativistic heavy-ion collisions is out of chemical equilibrium. It is
assumed that initially this matter is mostly composed of gluons, but quarks and
antiquarks are produced at later times. The dynamical evolution of partonic
system is described by the Bjorken-like ideal hydrodynamics with a time
dependent quark fugacity. The results of this model are compared with those
obtained by assuming the complete chemical equilibrium of partons already at
the initial stage. It is shown that in a chemically non-equilibrium scenario
the entropy gradually increases, and about 25% of the total final entropy is
generated during the hydrodynamic evolution of deconfined matter. We argue that
the (anti)quark suppression included in this approach may be responsible for
reduced (anti)baryon to meson ratios observed in heavy-ion collisions at LHC
energies.Comment: 19 pages, 6 figures, minor changes to match published versio
