Determining transport coefficients for a microscopic simulation of a hadron gas

Pratt, Scott; Baez, Alexander; Kim, Jane

doi:10.1103/physrevc.95.024901

Cited by 9 publications

(18 citation statements)

References 57 publications

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“…For further evidence, let us look at the relation between the relaxation time τ and the inverse of the scattering rate, the mean-free time τ mf t . In the case of no resonances [52] the relaxation time increases linearly with the collision time, with a proportionality factor of order 1. As seen on the bottom panel of Fig.…”

Section: Discussion and Comparisonmentioning

confidence: 99%

“…The results of existing studies in this range disagree up to a factor of ten and our goal is to understand the discrepancy between them. This question has recently also been addressed in [52], where the authors find a considerable difference between the results from the UrQMD transport code [48] (to which SMASH is closer in conception), and the ones from the B3D transport approach [52,53]. To get a better understanding of the differences between these approaches, we perform numerical solutions of the Boltzmann equation for simple systems using the Chapman-Enskog expansion including genuine 2 → 2 collisions [25].…”

Section: Introductionmentioning

confidence: 95%

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Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

et al. 2018

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We address a discrepancy between different computations of η/s (shear viscosity over entropy density) of hadronic matter. Substantial deviations of this coefficient are found between transport approaches mainly based on resonance propagation with finite lifetime and other (semi-analytical) approaches with energy-dependent cross-sections, where interactions do not introduce a timescale. We provide an independent extraction of this coefficient by using the newly-developed SMASH (Simulating Many Accelerated Strongly interacting Hadrons) transport code, which is an example of a mainly resonance-based approach. We compare the results from SMASH with numerical solutions of the Boltzmann equation for simple systems using the Chapman-Enskog expansion, as well as previous results in the literature. Our conclusion is that the hadron interaction via resonance formation/decay strongly affects the transport properties of the system, resulting in significant differences in η/s with respect to other approaches where binary collisions dominate. We argue that the relaxation time of the system -which characterizes the shear viscosity-is determined by the interplay between the mean-free time and the lifetime of resonances. We show how an artificial shortening of the resonance lifetimes, or the addition of a background elastic cross section nicely interpolate between the two discrepant results. arXiv:1709.03826v1 [nucl-th]

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Section: Discussion and Comparisonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 95%

Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

et al. 2018

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“…[45], the minimum of η/s, following RTA method, reaches the crossover temperature at 245 MeV. In a hydrodynamics-based transport model study [48], the estimated η/s near T = 160 MeV comes one-forth the value obtained in Ref. [46].…”

Section: Observablesmentioning

confidence: 99%

van der Waals hadron resonance gas and QCD phase diagram

Sarkar

Ghosh

2018

Phys. Rev. C

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Taking into account the recently developed van der Waals (VDW)-like equation of state (EoS) for grand canonical ensemble of fermions, the temperature-dependent profiles of normalized entropy density (s/T 3 ) and the ratio of shear viscosity and entropy density (η/s) for hadron resonance gas have been evaluated. The VDW parameters, corresponding to interactions between (anti)baryons, have been obtained by contrasting lattice EoS for QCD matter at finite chemical potentials (μ B ) and for T 160 MeV. The temperature-and chemical-potentialdependent study of s/T 3 and η/s for hadron gas, by signaling onsets of first-order phase transition and crossover in the hadronic phase of QCD matter, helps in understanding the QCD phase diagram in the (T , μ B ) plane. An estimation of probable location of critical point matches predictions from other recent studies.

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“…There is currently great interest in the extraction of transport coefficients of hot and dense matter in the field of heavy ion physics. At temperatures lower than 170 MeV, in the hadron gas phase, previous studies of shear viscosity have however proven to be inconsistent with each other [1,2,3,4]. In [5], more extensive results are discussed and the discrepancy is resolved by identifying the effect of resonance lifetimes on relaxation dynamics.…”

Section: Introductionmentioning

confidence: 99%

Systematic errors in transport calculations of shear viscosity using the Green-Kubo formalism

Rose

Torres-Rincón

Oliinychenko

et al. 2018

J. Phys.: Conf. Ser.

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The purpose of this study is to provide a reproducible framework in the use of the Green-Kubo formalism to extract transport coefficients. More specifically, in the case of shear viscosity, we investigate the limitations and technical details of fitting the auto-correlation function to a decaying exponential. This fitting procedure is found to be applicable for systems interacting both through constant and energy-dependent cross-sections, although this is only true for sufficiently dilute systems in the latter case. We find that the optimal fit technique consists in simultaneously fixing the intercept of the correlation function and use a fitting interval constrained by the relative error on the correlation function. The formalism is then applied to the full hadron gas, for which we obtain the shear viscosity to entropy ratio.

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Determining transport coefficients for a microscopic simulation of a hadron gas

Cited by 9 publications

References 57 publications

Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

Shear viscosity of a hadron gas and influence of resonance lifetimes on relaxation time

van der Waals hadron resonance gas and QCD phase diagram

Systematic errors in transport calculations of shear viscosity using the Green-Kubo formalism

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