A Calculation of the Viscosity to Entropy Ratio of a Hadronic Gas

Muroya, Shin; Sasaki, Nobuo

doi:10.1143/ptp.113.457

Cited by 21 publications

(24 citation statements)

References 7 publications

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“…Instead, an effective value p sat , obtained from Equation 6 above, is used. Solving p sat from this equation completes the calculation of primary production in the pQCD + saturation model.…”

Section: Initial Conditionsmentioning

confidence: 99%

Hydrodynamic Models for Heavy Ion Collisions

Huovinen

Ruuskanen

2006

Annu. Rev. Nucl. Part. Sci.

364

373

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Section: Initial Conditionsmentioning

confidence: 99%

Hydrodynamic Models for Heavy Ion Collisions

Huovinen

Ruuskanen

2006

Annu. Rev. Nucl. Part. Sci.

364

373

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“…Sophisticated Monte Carlo microscopic transport models, which include the full range of the hadronic spectrum (including resonances) [29], provide a far more realistic description of the hadronic matter created in relativistic heavy ion collisions. Several studies within those models have focused on equilibration and thermodynamic properties of infinite hadronic matter [30], and have extracted transport coefficients of hadronic gases [31,32], albeit none have performed a systematic study of η/s.In this Letter, we use a microscopic transport model known as the Ultrarelativistic Quantum Molecular Dynamics (UrQMD) model, described in [29,33], to sim- …”

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confidence: 99%

Shear-Viscosity to Entropy-Density Ratio of a Relativistic Hadron Gas

2009

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Ultrarelativistic heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) are thought to have produced a state of matter called the Quark-Gluon-Plasma, characterized by a very small shear viscosity to entropy density ratio η/s, near the lower bound predicted for that quantity by AntideSitter space/Conformal Field Theory (AdS/CFT) methods. As the produced matter expands and cools, it evolves through a phase described by a hadron gas with rapidly increasing η/s. We calculate η/s as a function of temperature in this phase and find that its value poses a challenge for viscous relativistic hydrodynamics, which requires small values of η/s throughout the entire evolution of the reaction in order to successfully describe the collective flow observables at RHIC. We show that the inclusion of non-unit fugacities will reduce η/s in the hadronic phase, yet not sufficiently to be compatible with viscous hydrodynamics. We therefore conclude that the origin of the low viscosity matter at RHIC must be in the partonic phase of the reaction.Ultrarelativistic heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are thought to have produced a Quark Gluon Plasma (QGP) with the characteristics of a near ideal fluid [1,2,3,4]. One of the most important current challenges in QGP research is to quantify the transport coefficients of this novel state of matter. Recently, attention in the field has been primarily focused on the shear viscosity to entropy density ratio η/s. Certain supersymmetric gauge theories with gravity duals [5] suggest a lower bound of η min = s/4π for this quantity, often referred to as the KSS bound [6]. Relativistic viscous hydrodynamic calculations require very low values of η/s in order to reproduce the RHIC elliptic flow (v 2 ) data [7,8,9]. However, current calculations assume a fixed value of η/s throughout the entire evolution of the system and neglect its temperature dependence. The exact value of η/s in these calculations is only known within a factor of ≈ 3, due to systematic uncertainties related to the choice of equation of state and initial conditions used [9,10]. A viscous hydrodynamical analysis [9] finds that η/s should lie within a range of 0.08-0.24 depending upon the choice of initial conditions and equation of state. This finding is supported by calculations of η/s for pure gluonic QCD, which yield values close to the KSS bound, and indirect estimates of η/s from calculations of the diffusion of heavy quarks, elliptic flow measurements, and transverse momentum correlations that arrive at roughly comparable values [11,12,13,14,15].Note that the shear viscosity of matter in a relativistic heavy ion collision is a time-dependent quantity. While the partonic phase of such a collision is expected to have a very low value of η/s, after hadronization occurs η/s is expected to rapidly increase. In order to quantitatively constrain the viscosity of the deconfined phase of a relativistic heavy ion collision, a separate calculation of the hadronic viscosity is necessary. Several i...

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“…For weakly coupled QGP perturbative results have been obtained by Arnold, Moore and Yaffe [226,227,228]. Microscopic transport models have helped to estimate transport coefficients of a hadron gas [229,230,231] and a parton gas [232,233]. The results seem to indicate that η/s from a hadron gas is larger than the KSS bound 1/(4π) [181] which is proposed by the AdS/CFT correspondence.…”

Section: Qcd and Hydrodynamicsmentioning

confidence: 99%

Evaluating results from the Relativistic Heavy Ion Collider with perturbative QCD and hydrodynamics

Fries

Nonaka

2011

Progress in Particle and Nuclear Physics

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We review the basic concepts of perturbative quantum chromodynamics (QCD) and relativistic hydrodynamics, and their applications to hadron production in high energy nuclear collisions. We discuss results from the Relativistic Heavy Ion Collider (RHIC) in light of these theoretical approaches. Perturbative QCD and hydrodynamics together explain a large amount of experimental data gathered during the first decade of RHIC running, although some questions remain open. We focus primarily on practical aspects of the calculations, covering basic topics like perturbation theory, initial state nuclear effects, jet quenching models, ideal hydrodynamics, dissipative corrections, freeze-out and initial conditions. We conclude by comparing key results from RHIC to calculations.

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A Calculation of the Viscosity to Entropy Ratio of a Hadronic Gas

Cited by 21 publications

References 7 publications

Hydrodynamic Models for Heavy Ion Collisions

Hydrodynamic Models for Heavy Ion Collisions

Shear-Viscosity to Entropy-Density Ratio of a Relativistic Hadron Gas

Evaluating results from the Relativistic Heavy Ion Collider with perturbative QCD and hydrodynamics

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