Causality violations in cascade models of nuclear collisions

Kortemeyer, Gerd; Bauer, Wolfgang; Haglin, Kevin; Murray, Joelle; Pratt, Scott

doi:10.1103/physrevc.52.2714

Cited by 35 publications

(59 citation statements)

References 16 publications

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“…The flow-asymmetry vanishes when the calculation is performed in the c.m.-frame, which is what we did in this work. The geometry-based code did not appear to be sensitive to this asymmetry, however, Lorentz invariance certainly still is an issue [13].…”

Section: Results and Conclusionmentioning

confidence: 99%

Nuclear flow in consistent Boltzmann algorithm models

Kortemeyer¹,

Daffin²,

Bauer³

1996

Physics Letters B

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We investigate the stochastic Direct Simulation Monte Carlo method (DSMC) for numerically solving the collision-term in heavy-ion transport theories of the Boltzmann-Uehling-Uhlenbeck (BUU) type. The first major modification we consider is changes in the collision rates due to excluded volume and shadowing/screening effects (Enskog theory). The second effect studied by us is the inclusion of an additional advection term. These modifications ensure a non-vanishing second virial and change the equation of state for the scattering process from that of an ideal gas to that of a hard-sphere gas. We analyse the effect of these modifications on the calculated value of directed nuclear collective flow in heavy ion collisions, and find that the flow slightly increases.

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Section: Results and Conclusionmentioning

confidence: 99%

Nuclear flow in consistent Boltzmann algorithm models

Kortemeyer¹,

Daffin²,

Bauer³

1996

Physics Letters B

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“…In fact such a description has some shortcomings concerning causality violations which have been pointed out for example in Ref. [35]. Especially for the algorithm presented above we have to face the fact that the collision times of colliding particles are different in the lab frame.…”

Section: A the Geometrical Methodsmentioning

confidence: 99%

“…In spite of this definition the covariance of the Boltzmann equation is still not fulfilled, because the time ordering of collisions might be changed under Lorentz transformation [34,35].…”

Section: A the Geometrical Methodsmentioning

confidence: 99%

“…It turns out that in dense matter when the interaction length σ/π is not much smaller than the mean free path of particles, causality violation [34,35] will arise in these cascade models and will lead to numerical artifacts [36,37]. One way to reduce these artifacts is to apply the common test particle method (or "particle subdivisions") [38,39], in which the interaction length of the test particles is reduced by √ N test , while the mean free path is unchanged.…”

Section: Introductionmentioning

confidence: 99%

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Thermalization of gluons in ultrarelativistic heavy ion collisions by including three-body interactions in a parton cascade

2005

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We develop a new 3+1 dimensional Monte Carlo cascade solving the kinetic on-shell Boltzmann equations for partons including the inelastic gg ↔ ggg pQCD processes. The back reaction channel is treated -for the first time -fully consistently within this scheme. An extended stochastic method is used to solve the collision integral. The frame dependence and convergency are studied for a fixed tube with thermal initial conditions. The detailed numerical analysis shows that the stochastic method is fully covariant and that convergency is achieved more efficiently than within a standard geometrical formulation of the collision term, especially for high gluon interaction rates. The cascade is then applied to simulate parton evolution and to investigate thermalization of gluons for a central Au+Au collision at RHIC energy. For this study the initial conditions are assumed to be generated by independent minijets with p T > p 0 = 2 GeV. With that choice it is demonstrated that overall kinetic equilibration is driven mainly by the inelastic processes and is achieved on a scale of 1 fm/c. The further evolution of the expanding gluonic matter in the central region then shows almost an ideal hydrodynamical behavior. In addition, full chemical equilibration of the gluons follows on a longer timescale of about 3 fm/c. *

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“…The problem of superluminous signals has been studied in Ref. 155) In this geometrical method for two body collision, collision occurs in the separated points, which is the same as action-at-distance interaction. In order to solve this problem, one can use the "full-ensemble" method or "subdivision" technique 156), 144), 146) in which cross section is reduced by the factor of the number of test (over sampling) particle σ/N test in order to recover the local nature of Boltzmann collision term in the limit of N test → ∞.…”

Section: Scattering Algorithmsmentioning

confidence: 99%

Dynamical modeling of high energy heavy ion collisions

Hirano

Nara

2012

Progress of Theoretical and Experimental Physics

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We present theoretical approaches to high energy nuclear collisions in detail putting a special emphasis on technical aspects of numerical simulations. Models include relativistic hydrodynamics, Monte-Carlo implementation of kT -factorization formula, jet quenching in expanding fluids, a hadronic transport model and the Vlasov equation for colored particles. §1. IntroductionOne of the primary purposes of heavy ion physics at ultrarelativistic energies is to explore properties of strongly interacting matter at high temperature and densities, namely, the quark gluon plasma (QGP). 2), 3), 1) To this purpose, collider experiments of high energy pp, dA and AA collisions have been performed at both Relativistic Heavy Ion Collider (RHIC) in Brookhaven National Laboratory (BNL) and Large Hadron Collider (LHC) in European Organization for Nuclear Research (CERN). It is of particular importance to comprehensively understand space-time evolution of matter created in high energy heavy ion collisions so that one can extract information on the detailed properties of matter from experimental data.High energy nuclear collisions contain rich physics and exhibit many aspects of dynamics according to relevant energy and time scales. Collisions of two energetic nuclei can be viewed as those of highly coherent dense gluons. Universal behaviors of hadrons and nuclei at the high energy limit are called the color glass condensate (CGC). 4) Just after the collision, longitudinal color electric and magnetic fields between the two passing nuclei, which is called color flux tubes, 5) are produced from CGC initial conditions. Subsequent evolution of these flux tubes is called "glasma". 6) Long range rapidity correlations in the glasma 7), 8), 9) provide a natural explanation for the ridge structure observed at RHIC 10), 11) and LHC. 12) It was pointed out that instabilities of the gluon fields could play a significant role in the process of thermalization. 13), 14), 15)A model based on k T -factorization formula 20), 21), 16), 17), 18), 19), 22), 24), 23) or classical Yang-Mills approach 25), 26) reproduces the multiplicity distribution for charged hadrons at RHIC and LHC. However, initial transverse energy per particle is large compared with the experimental data. 27), 26), 24) Glasma evolution based on a 2+1 dimensional classical Yang-Mills simulation does not account for elliptic flow data at RHIC. 28) These facts suggest the necessity of inclusion of further evolution with much stronger interaction, e.g., hydrodynamical evolution. Indeed, a nearly perfect fluid picture 29), 30), 31), 32), 33) turns out to explain large elliptic flow 34) observed at RHIC 35), 36), 37) and LHC, 38), 39), 40) which leads to establishment of a new paradigm typeset using PTPT E X.cls Ver.0.9

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Causality violations in cascade models of nuclear collisions

Cited by 35 publications

References 16 publications

Nuclear flow in consistent Boltzmann algorithm models

Nuclear flow in consistent Boltzmann algorithm models

Thermalization of gluons in ultrarelativistic heavy ion collisions by including three-body interactions in a parton cascade

Dynamical modeling of high energy heavy ion collisions

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