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We study anisotropic fluid dynamics derived from the Boltzmann equation based on a particular choice for the anisotropic distribution function within a boost-invariant expansion of the fluid in one spatial dimension. In order to close the conservation equations we need to choose an additional moment of the Boltzmann equation. We discuss the influence of this choice of closure on the time evolution of fluid-dynamical variables and search for the best agreement to the solution of the Boltzmann equation in the relaxation-time approximation. [ABSTRACT FROM AUTHOR]

We review the results from the event-by-event next-to-leading order perturbative QCD + saturation + viscous hydrodynamics (EbyE NLO EKRT) model. With a simultaneous analysis of LHC and RHIC bulk observables we systematically constrain the QCD matter shear viscosity-to-entropy ratio η / s ( T ) , and test the initial state computation. In particular, we study the centrality dependences of hadronic multiplicities, p T spectra, flow coefficients, relative elliptic flow fluctuations, and various flow-correlations in 2.76 and 5.02 TeV Pb+Pb collisions at the LHC and 200 GeV Au+Au collisions at RHIC. Overall, our results match remarkably well with the LHC and RHIC measurements, and predictions for the 5.02 TeV LHC run are in an excellent agreement with the data. We probe the applicability of hydrodynamics via the average Knudsen numbers in the space-time evolution of the system and viscous corrections on the freeze-out surface. [ABSTRACT FROM AUTHOR]

Abstract: We investigate a fluid dynamical response to the fluctuations and geometry of the initial state density profiles in ultrarelativistic heavy ion collisions. [Copyright &y& Elsevier]

Relativistic dissipative fluid dynamics is a common tool to describe the space-time evolution of the strongly interacting matter created in ultrarelativistic heavy-ion collisions. For a proper comparison to experimental data, fluid-dynamical calculations have to be performed on an event-by-event basis. Therefore, fluid dynamics should be able to reproduce, not only the event-averaged momentum anisotropies, ‹νn〉, but also their distributions. In this paper, we investigate the event-by-event distributions of the initial-state and momentum anisotropies Ɛn and νn, and their correlations. We demonstrate that the event-by-event distributions of relative νn fluctuations are almost equal to the event-by-event distributions of corresponding Ɛn fluctuations, allowing experimental determination of the relative anisotropy fluctuations of the initial state. Furthermore, the correlation c(ν2,ν4) turns out to be sensitive to the viscosity of the fluid providing an additional constraint to the properties of the strongly interacting matter. [ABSTRACT FROM AUTHOR]

We present numerical methods to solve the Israel–Stewart (IS) equations of causal relativistic dissipative fluid dynamics with bulk and shear viscosities. We then test these methods studying the Riemann problem in (1+1)- and (2+1)-dimensional geometry. The numerical schemes investigated here are applicable to realistic (3+1)-dimensional modeling of a relativistic dissipative fluid. [ABSTRACT FROM AUTHOR]

Background: Experimental data from heavy-ion experiments at RHIC-BNL and LHC-CERN are quantitatively described using relativistic fluid dynamics. Even p+A and p+p collisions show signs of collective behavior describable in the same manner. Nevertheless, small system sizes and large gradients strain the limits of applicability of fluid-dynamical methods. Purpose: The range of applicability of fluid dynamics for the description of the collective behavior, and in particular of the elliptic flow, of small systems needs to be explored. Method: Results of relativistic fluid-dynamical simulations are compared with solutions of the Boltzmann equation in a longitudinally boost-invariant picture. As the initial condition, several different transverse energy-density profiles for equilibrated matter are investigated. Results: While there is overall a fair agreement of energy- and particle-density profiles, components of the shear-stress tensor are more sensitive to details of the implementation. The highest sensitivity is exhibited by quantities influenced by properties of the medium at freeze-out. Conclusions: For some quantities, like the shear-stress tensor, agreement between fluid dynamics and transport theory extends into regions of Knudsen numbers and inverse Reynolds numbers where relativistic fluid dynamics is believed to fail. [ABSTRACT FROM AUTHOR]

Abstract: Using next-to-leading order perturbative QCD and a conjecture of saturation to suppress the production of low-energy partons, we calculate the initial energy densities and formation times for the dissipative fluid dynamical evolution of the quark–gluon plasma produced in ultrarelativistic heavy-ion collisions. We identify the model uncertainties and demonstrate the predictive power of the approach by a good global agreement with the measured centrality dependence of charged particle multiplicities, transverse momentum spectra and elliptic flow simultaneously for the Pb+Pb collisions at the LHC and Au+Au at RHIC. In particular, the shear viscosity in the different phases of QCD matter is constrained in this new model simultaneously by all these data. [Copyright &y& Elsevier]

We study the transverse spectra of hadrons in nearly central AA collisions at RHIC and LHC in a broad transverse momentum range [K.J. Eskola, H. Honkanen, H. Niemi, P.V. Ruuskanen and S.S. Räsänen, arXiv:hep-ph/0506049]. Low-p T spectra are calculated by using boost-invariant hydrodynamics with initial energy and net-baryon densities from the EKRT [K.J. Eskola, K. Kajantie, P.V. Ruuskanen and K. Tuominen, Nucl. Phys. B 570 (2000) 379 [arXiv:hep-ph/9909456]] pQCD+saturation model. High-p T spectra are obtained from pQCD jet calculation [K.J. Eskola and H. Honkanen, Nucl. Phys. A 713 (2003) 167 [arXiv:hep-ph/0205048]] including the energy loss of the parton [K.J. Eskola, H. Honkanen, C.A. Salgado and U.A. Wiedemann, Nucl. Phys. A 747 (2005) 511 [arXiv:hep-ph/0406319]] in the matter prior to its fragmentation to final hadrons. [Copyright &y& Elsevier]