Hot Spots and Turbulent Initial Conditions of Quark-Gluon Plasmas in Nuclear Collisions

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Abstract
As a result of multiple mini-jet production, initial conditions of the QCD plasma formed in ultrarelativistic nuclear collisions may be inhomogeneous, with large fluctuations of the local energy density (hot spots), and turbulent, with a chaotic initial transverse velocity field. Assuming rapid local thermalization, the evolution of such plasmas is computed using longitudinal boost-invariant 3+1-dimensional hydrodynamics. We compare the evolution in case that the speed of sound in the plasma is constant to one resulting from an equation of state involving a strong first order transition, with a minimum of the velocity of sound as a function of energy density. We find that azimuthally asymmetric fluctuations and correlations of the transverse energy flow can develop in both cases due to the initial inhomogeneities. Hot spots also enhance significantly high-transverse momenta direct photon yields. In the case with a phase transition, the hadronization surface evolves into an unusual foam-like structure. Also in that case, we find that hadronization is considerably delayed relative to the ideal gas case, just as previous studies have found for homogeneous initial conditions. The time-delay signature of a rapid cross-over transition region in the QCD equation of state (as observable via meson interferometry) is thus found to be remarkably robust to uncertainties in the initial conditions in heavy-ion reactions.

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