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Dynamics of anisotropic plasma at the early stages of relativistic heavy-ion collisions

We discuss the evolution of anisotropic boost-invariant quark-gluon plasma possibly created at the early stages of relativistic heavy-ion collisions. Our considerations are based on the recently proposed formalism that is an extension of the relativistic perfect-fluid hydrodynamics. We analyze i) the pure partonic system described by the anisotropic phase-space distribution function and ii) the system of partons interacting with the local magnetic fields. The second analysis is a simplified attempt to include the effects of color fields on the particle dynamics. Our model results are discussed in the context of early thermalization and isotropization. Under general assumptions of the particle, energy, and momentum conservations we show that for large evolution times the ratio of the longitudinal and transverse pressures of the pure partonic system tends to zero. Hence, the system with the initial momentum distribution elongated along the beam axis always passes through the isotropic stage where the transverse and longitudinal pressures are equal. The inclusion of the magnetic field in this case gives negative contribution to the longitudinal pressure, hence the transient stage when the total longitudinal and transverse pressures become equal may be reached earlier, depending on the strength of the field.