Collective flow in single-hit QCD kinetic theory

Kurkela, Aleksi; Mazeliauskas, Aleksas; Törnkvist, Robin

doi:10.1007/jhep11(2021)216

Cited by 21 publications

(5 citation statements)

References 52 publications

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“…This numerical integration has been crosschecked against the code used in e.g. [28]. The results of the comparison of the full numerical integration are shown in Tables 1 and 2 for Boltzmann and Bose-Einstein/Fermi-Dirac distributions, respectively.…”

Section: The Thermal Equilibrium Casementioning

confidence: 99%

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AMY Lorentz invariant parton cascade: the thermal equilibrium case

Kurkela,

Törnkvist,

Zapp

2024

Eur. Phys. J. C

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We introduce the parton cascade Alpaca, which evolves parton ensembles corresponding to single events according to the effective kinetic theory of QCD at high temperature formulated by Arnold, Moore and Yaffe by explicitly simulating elastic scattering, splitting and merging. By taking the ensemble average over many events the phase space density (as evolved by the Boltzmann equation) is recovered, but the parton cascade can go beyond the evolution of the mean because it can be turned into a complete event generator that produces fully exclusive final states including fluctuations and correlations. The parton cascade does not require the phase space density as input (except for the initial condition at the starting time). Rather, effective masses and temperature, which are functions of time and are defined as integrals over expressions involving the distribution function, are estimated in each event from just the parton ensemble of that event. We validate the framework by showing that ensembles sampled from a thermal distribution stay in thermal equilibrium even after running the simulation for a long time. This is a non-trivial result, because it requires all parts of the simulation to intertwine correctly.

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Section: The Thermal Equilibrium Casementioning

confidence: 99%

“…In the latter case it can be studied using the effective kinetic theory of QCD by Arnold, Moore and Yaffe (AMY) [23][24][25], describing the dynamics of quarks of gluons. Kinetic theory is a natural candidate for the description of small collision systems [26][27][28][29], since it is valid in-and out-of-equilibrium.…”

Section: Introductionmentioning

confidence: 99%

AMY Lorentz invariant parton cascade: the thermal equilibrium case

Kurkela,

Törnkvist,

Zapp

2024

Eur. Phys. J. C

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“…On the theory front, the non-equilibrium dynamics of QCD and QCD-like theories have been investigated using kinetic theory, classical field simulations, and gauge/gravity duality (see [6,7] for recent reviews). There is a growing appreciation that the off-equilibrium dynamics in the early stages of heavy ion collisions may be crucial for understanding the observed collectivity [8][9][10][11], especially in smaller collision systems. QCD effective kinetic theory (EKT) [12] has become a particularly important tool for understanding far-fromequilibrium dynamics and thermalization in QCD (see e.g.…”

Section: Introductionmentioning

confidence: 99%

Scaling and adiabaticity in a rapidly expanding gluon plasma

Brewer,

Scheihing-Hitschfeld,

Yin

2022

Preprint

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In this work we aim to gain qualitative insight on the far-from-equilibrium behavior of the gluon plasma produced in the early stages of a heavy-ion collision. It was recently discovered [1] that the distribution functions of quarks and gluons in QCD effective kinetic theory (EKT) exhibit self-similar "scaling" evolution with time-dependent scaling exponents long before those exponents reach their pre-hydrodynamic fixed-point values.In this work we shed light on the origin of this time-dependent scaling phenomenon in the small-angle approximation to the Boltzmann equation. We first solve the Boltzmann equation numerically and find that time-dependent scaling is a feature of this kinetic theory, and that it captures key qualitative features of the scaling of hard gluons in QCD EKT. We then proceed to study scaling analytically and semi-analytically in this equation. We find that an appropriate momentum rescaling allows the scaling distribution to be identified as the instantaneous ground state of the operator describing the evolution of the distribution function, and the approach to the scaling function is described by the decay of the excited states. That is to say, there is a frame in which the system evolves adiabatically. Furthermore, from the conditions for adiabaticity we can derive evolution equations for the time-dependent scaling exponents. In addition to the known free-streaming and BMSS fixed points, we identify a new "dilute" fixed point when the number density becomes small before hydrodynamization. Corrections to the fixed point exponents in the small-angle approximation agree quantitatively with those found previously in QCD EKT and arise from the evolution of the ratio between hard and soft scales.

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“…The description beyond HR, in general, can be exceeding complex. It is commonly assumed that dynamics in such situations involve a tower of nonhydrodynamic excitations [5,6].…”

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confidence: 99%

“…In smaller colliding systems, eccentricities are dominated by shorter scale fluctuations and the EHR response can be responsible for v n generation. In fact, describing observed collectivity in those small colliding systems from non-hydrodynamic transport has already attracted considerable attentions [5,6]. Besides, medium response to jet propagation can be another channel to probe the EHR behavior.…”

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confidence: 99%