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Azwinndini Muronga

Publications and source records attributed to Azwinndini Muronga.

26 records · Page 2Linked to original sources
arXiv2007

Relativistic Dynamics of Non-ideal Fluids: Viscous and heat-conducting fluids II. Transport properties and microscopic description of relativistic nuclear matter

In the causal theory of relativistic dissipative fluid dynamics, there are conditions on the equation of state and other thermodynamic properties such as the second-order coefficients of a fluid that need to be satisfied to guarantee that the fluid perturbations propagate causally and obey hyperbolic equations. The second-order coefficients in the causal theory, which are the relaxation times for the dissipative degrees of freedom and coupling constants between different forms of dissipation (relaxation lengths), are presented for partonic and hadronic systems. These coefficients involves relativistic thermodynamic integrals. The integrals are presented for general case and also for different regimes in the temperature--chemical potential plane. It is shown that for a given equation of state these second-order coefficients are not additional parameters but they are determined by the equation of state. We also present the prescription on the calculation of the freeze-out particle spectra from the dynamics of relativistic non-ideal fluids.

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arXiv2004

Evolution of Hot, Dissipative Quark Matter in Relativistic Nuclear Collisions

Non-ideal fluid dynamics with cylindrical symmetry in transverse direction and longitudinal scaling flow is employed to simulate the space-time evolution of the quark-gluon plasma produced in heavy-ion collisions at RHIC energies. The dynamical expansion is studied as a function of initial energy density and initial time. A causal theory of dissipative fluid dynamics is used instead of the standard theories which are acausal. We compute the parton momentum spectra and HBT radii from two-particle correlation functions. We find that, in non-ideal fluid dynamics, the reduction of the longitudinal pressure due to viscous effects leads to an increase of transverse flow and a decrease of the ratio $R_{out}/R_{side}$ as compared to the ideal fluid approximation.

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arXiv2003

Causal Theories of Dissipative Relativistic Fluid Dynamics for Nuclear Collisions

Non-equilibrium fluid dynamics derived from the extended irreversible thermodynamics of the causal Müller--Israel--Stewart theory of dissipative processes in relativistic fluids based on Grad's moment method is applied to the study of the dynamics of hot matter produced in ultra--relativistic heavy ion collisions. The temperature, energy density and entropy evolution are investigated in the framework of the Bjorken boost--invariant scaling limit. The results of these second order theories are compared to those of first order theories due to Eckart and to Landau and Lifshitz and those of zeroth order (perfect fluid) due to Euler. In the presence of dissipation perfect fluid dynamics is no longer valid in describing the evolution of the matter. First order theories fail in the early stages of evolution. Second order theories give a better description in good agreement with transport models. It is shown in which region the Navier--Stokes--Fourier laws (first order theories) are a reasonable limiting case of the more general extended thermodynamics (second order theories).

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arXiv2003

Shear Viscosity Coefficient from Microscopic Models

The transport coefficient of shear viscosity is studied for a hadron matter through microscopic transport model, the Ultra--relativistic Quantum Molecular Dynamics (UrQMD), using the Green--Kubo formulas. Molecular--dynamical simulations are performed for a system of light mesons in a box with periodic boundary conditions. Starting from an initial state composed of $π, η,ω,ρ,ϕ$ with a uniform phase--space distribution, the evolution takes place through elastic collisions, production and annihilation. The system approaches a stationary state of mesons and their resonances, which is characterized by common temperature. After equilibration, thermodynamic quantities such as the energy density, particle density, and pressure are calculated. From such an equilibrated state the shear viscosity coefficient is calculated from the fluctuations of stress tensor around equilibrium using Green--Kubo relations. We do our simulations here at zero net baryon density so that the equilibration times depend on the energy density. We do not include hadron strings as degrees of freedom so as to maintain detailed balance. Hence we do not get the saturation of temperature but this leads to longer equilibration times.

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arXiv2002

Second Order Dissipative Fluid Dynamics for Ultra-Relativistic Nuclear Collisions

The Müller-Israel-Stewart second order theory of relativistic imperfect fluids based on Grad's moment method is used to study the expansion of hot matter produced in ultra-relativistic heavy ion collisions. The temperature evolution is investigated in the framework of the Bjorken boost-invariant scaling limit. The results of these second-order theories are compared to those of first-order theories due to Eckart and to Landau and Lifshitz and those of zeroth order (perfect fluid) due to Euler.

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arXiv2001

Dissipative Relativistic Fluid Dynamics for Nuclear Collisions

In the context of the Müller-Israel-Stewart second-order theory for dissipative fluids due to Grad, we analyze the effects of thermal conduction and viscosity in heavy ion collisions. We contrast the results to those of the first-order theory due to Eckart and to Landau and Lifshitz and to those of perfect (ideal) fluid due to Euler. We study the energy density and entropy density evolution of a pion gas produced in the heavy ion collisions. The truncated version of the second-order theory is used to find the dissipative quantities.

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