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| Format: | Preprint |
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2026
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| Online-Zugang: | https://arxiv.org/abs/2604.25059 |
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| _version_ | 1866913067141431296 |
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| author | Ohanaka, Okey Lin, Zi-Wei |
| author_facet | Ohanaka, Okey Lin, Zi-Wei |
| contents | We use the Chapman-Enskog method to investigate the shear viscosity of the quark-gluon plasma with a focus on its relation to parton cross sections. We use the recently obtained analytical expression for the shear viscosity $η$ of a massless quark-gluon gas at chemical equilibrium with Boltzmann statistics and all $2\leftrightarrow 2$ scatterings with arbitrary cross sections. Here we apply this general expression to cross sections at finite temperature that are based on perturbative-QCD and screened with scaled thermal masses $\sqrtκ\,m_D$ and $\sqrtκ\,m_F$. We find that the Chapman-Enskog results on $η\, g^4/T^3$ versus $m_D/T$ at $κ=1$ are qualitatively similar to but higher than the corresponding leading-order results from the AMY framework. We then find that using $κ=0.4$ allows the Chapman-Enskog results to match well the corresponding AMY results as it includes the effect of using thermal masses (instead of self-energies) to screen the cross sections. In addition, we show that the shear viscosity-to-entropy density ratio $η/s$ is very sensitive to the choice of momentum scale $Q$ in the strong coupling, where the choice of $Q=3T$ leads to $η/s \sim 0.15$ for $N_f=0$ or 3 at the QCD phase transition temperature $T_c$. These results lay the foundation for mapping parton cross sections to given shear viscosity in parton transport models and QCD effective kinetic theory. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2604_25059 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Chapman-Enskog calculation of the shear viscosity of quark-gluon plasma including all $2\leftrightarrow 2$ scatterings at finite temperature Ohanaka, Okey Lin, Zi-Wei Nuclear Theory High Energy Physics - Phenomenology We use the Chapman-Enskog method to investigate the shear viscosity of the quark-gluon plasma with a focus on its relation to parton cross sections. We use the recently obtained analytical expression for the shear viscosity $η$ of a massless quark-gluon gas at chemical equilibrium with Boltzmann statistics and all $2\leftrightarrow 2$ scatterings with arbitrary cross sections. Here we apply this general expression to cross sections at finite temperature that are based on perturbative-QCD and screened with scaled thermal masses $\sqrtκ\,m_D$ and $\sqrtκ\,m_F$. We find that the Chapman-Enskog results on $η\, g^4/T^3$ versus $m_D/T$ at $κ=1$ are qualitatively similar to but higher than the corresponding leading-order results from the AMY framework. We then find that using $κ=0.4$ allows the Chapman-Enskog results to match well the corresponding AMY results as it includes the effect of using thermal masses (instead of self-energies) to screen the cross sections. In addition, we show that the shear viscosity-to-entropy density ratio $η/s$ is very sensitive to the choice of momentum scale $Q$ in the strong coupling, where the choice of $Q=3T$ leads to $η/s \sim 0.15$ for $N_f=0$ or 3 at the QCD phase transition temperature $T_c$. These results lay the foundation for mapping parton cross sections to given shear viscosity in parton transport models and QCD effective kinetic theory. |
| title | Chapman-Enskog calculation of the shear viscosity of quark-gluon plasma including all $2\leftrightarrow 2$ scatterings at finite temperature |
| topic | Nuclear Theory High Energy Physics - Phenomenology |
| url | https://arxiv.org/abs/2604.25059 |