Abstract
We investigate viscous effects on the dynamical evolution of QCD matter during the first-order phase transition, which may happen in heavy-ion collisions. We first obtain the first-order phase transition line in the QCD phase diagram under the Gibbs condition by using the MIT bag model and the hadron resonance gas model for the equation of state of partons and hadrons. The viscous pressure, which corresponds to the friction in the energy balance, is then derived from the energy and net baryon number conservation during the phase transition. We find that the viscous pressure relates to the thermodynamic change of the two-phase state and thus affects the timescale of the phase transition. Numerical results are presented for demonstrations.
Highlights
A phase diagram separates phases and determines conditions, at which different phases coexist at thermal equilibrium
We investigate viscous effects on the dynamical evolution of QCD matter during the first-order phase transition, which may happen in heavy-ion collisions
At high baryon chemical potential, theory predicts a first-order phase transition line [3] ending at a QCD critical point [4]
Summary
A phase diagram separates phases and determines conditions, at which different phases coexist at thermal equilibrium. The phase transition of QCD matter can be investigated in experiments of heavy-ion collisions, where quark-gluon plasma (QGP) cools down due to expansion and hadronizes at certain temperature and baryon chemical potential. The QCD matter produced in heavy-ion collisions possesses, a nonzero viscosity [9,10,11] and deviates from thermal equilibrium. If the system is not far away from thermal equilibrium, one can still define thermodynamic quantities such as temperature, pressure, and chemical potential, as done in viscous hydrodynamic calculations. With these thermodynamic quantities one can identify the first-order phase transition for the expanding QGP, if the Gibbs condition holds. II we first calculate the first-order phase transition line under the Gibbs condition for phase equilibrium
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