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Register a new userKinetic evolution and correlation of fluctuations in an expanding quark gluon plasma
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Evolution of spatially anisotropic perturbation created in the system formed after Relativistic Heavy Ion Collisions has been studied. The microscopic evolution of the fluctuations has been examined within the ambit of Boltzmann Transport Equation (BTE) in a hydrodynamically expanding background. The expansion of the background composed of Quark Gluon Plasma (QGP) is treated within the framework of relativistic hydrodynamics. Spatial anisotropic fluctuations with different geometry have been evolved through Boltzmann equation. It is observed that the trace of such fluctuation survive the evolution. Within the relaxation time approximation analytical results have been obtained for the evolution of these anisotropies. Explicit relations between fluctuations and transport coefficients have been derived. The mixing of various Fourier (or $k$) modes of the perturbations during the evolution of the system has been explicitly demonstrated. This study is very useful in understanding the presumption that the measured anisotropies in the data from heavy ion collisions at relativistic energies imitate the initial state effects. The evolution of correlation function for the perturbation in pressure has been studied and shown that the initial correlation between two neighbouring points in real space evolves to a constant value at later time which gives rise to Dirac delta function for the correlation function in Fourier space. The power spectrum of the fluctuation in thermodynamic quantities (like temperature estimated in this work) can be connected to the fluctuation in transverse momentum of the thermal hadrons measured experimentally. The bulk viscous coefficient of the QGP has been estimated by using correlations of pressure fluctuation with the help of Green-Kubo relation. Angular power spectrum of the anisotropies has been estimated in the appendix.
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We argue that an expanding quark-gluon plasma has an anomalous viscosity, which arises from interactions with dynamically generated colour fields. The anomalous viscosity dominates over the collisional viscosity for large velocity gradients or weak coupling. This effect may provide an explanation for the apparent near perfect liquidity of the matter produced in nuclear collisions at RHIC without the assumption that it is a strongly coupled state.
We propose a new scenario characterizing the transition of the quark-gluon plasma (QGP) produced in heavy-ion collisions from a highly non-equilibrium state at early times toward a fluid described by hydrodynamics at late times. We develop an analogy to the evolution of a quantum mechanical system that is governed by the instantaneous ground states. In the simplest case, these slow modes are pre-hydrodynamic in the sense that they are initially distinct from, but evolve continuously into, hydrodynamic modes. For a class of collision integrals, the pre-hydrodynamic mode represents the angular distribution (in momentum space) of those gluons that carry most of the energy. We illustrate this scenario using a kinetic description of weakly-coupled Bjorken expanding plasma. Rapid longitudinal expansion drives a reduction in the degrees of freedom at early times. In the relaxation time approximation for the collision integral, we show quantitatively that the full kinetic theory evolution is dominated by the pre-hydrodynamic mode. We elaborate on the criterion for the dominance of pre-hydrodynamic slow modes and speculate that adiabatic hydrodynamization may describe the pre-equilibrium behavior of the QGP produced in heavy-ion collisions.
Averaged over ensemble of initial conditions kinetic transport equations of weakly coupled systems of quarks and gluons are derived. These equations account for the correlators of fluctuations of particles and classical gluon fields. The isotropization of particle momenta by field fluctuations at the early prethermal stage of matter evolution in ultrarelativistic heavy ion collisions is discussed. Our results can be useful for understanding under what conditions isotropization of the quark-gluon plasma in ultrarelativistic heavy ion collisions can be reached within phenomenologically observed time scales.
The interaction of heavy flavor with the quark-gluon plasma (QGP) in relativistic heavy-ion collisions is studied using JETSCAPE, a publicly available software package containing a framework for Monte Carlo event generators. Multi-stage (and multi-model) evolution of heavy quarks within JETSCAPE provides a cohesive description of heavy flavor quenching inside the QGP. As the parton shower develops, a model becomes active as soon as its kinematic region of validity is reached. Two combinations of heavy-flavor energy-loss models are explored within a realistic QGP medium, using parameters which were tuned to describe {it light-flavor} partonic energy-loss.
Brief review of the hadronic probes that are used to diagnose the quark-gluon plasma produced in relativistic heavy ion collisions and interrogate its properties. Emphasis is placed on probes that have significantly impacted our understanding of the nature of the quark-gluon plasma and confirmed its formation.
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