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Temperature dependence of meson screening masses; a comparison of effective model with lattice QCD

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 نشر من قبل Masahiro Ishii
 تاريخ النشر 2015
  مجال البحث
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Temperature dependence of pion and sigma-meson screening masses is evaluated by the Polyakov-loop extended Nambu--Jona-Lasinio model with the entanglement vertex (EPNJL model). We propose a practical way of calculating meson screening masses in the NJL-type effective models. The method based on the Pauli-Villars regularization solves the well-known difficulty that the evaluation of screening masses is not easy in the NJL-type effective models. The method is applied to analyze temperature dependence of pion screening masses calculated with state-of-the-art lattice simulations with success in reproducing the lattice QCD results. We predict the temperature dependence of pole mass by using EPNJL model.

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Temperature dependence of pion and sigma-meson screening masses is evaluated by the Polyakov-loop extended Nambu--Jona-Lasinio (PNJL) model with the entanglement vertex. We propose a practical way of calculating meson screening masses in the NJL-type effective models. The method based on the Pauli-Villars regularization solves the well-known difficulty that the evaluaton of screening masses is not easy in the NJL-type effective models.The PNJL model with the entanglement vertex and the Pauli-Villars regularization well reproduces lattice QCD results on temperature dependence of the chiral condensate and the Polyakov loop. The method is applied to analyze temperature dependence of pion screening mass calculated with state-of-the-art lattice simulations with success in reproducing the lattice QCD results.
We propose a practical effective model by introducing temperature ($T$) dependence to the coupling strengths of four-quark and six-quark Kobayashi-Maskawa-t Hooft interactions in the 2+1 flavor Polyakov-loop extended Nambu-Jona-Lasinio model. The $T$ dependence is determined from LQCD data on the renormalized chiral condensate around the pseudocritical temperature $T_c^{chi}$ of chiral crossover and the screening-mass difference between $pi$ and $a_0$ mesons in $T > 1.1T_c^chi$ where only the $U(1)_{rm A}$-symmetry breaking survives. The model well reproduces LQCD data on screening masses $M_{xi}^{rm scr}(T)$ for both scalar and pseudoscalar mesons, particularly in $T ge T_c^{chi}$. Using this effective model, we predict meson pole masses $M_{xi}^{rm pole}(T)$ for scalar and pseudoscalar mesons. For $eta$ meson, the prediction is consistent with the experimental value at finite $T$ measured in heavy-ion collisions. We point out that the relation $M_{xi}^{rm scr}(T)-M_{xi}^{rm pole}(T) approx M_{xi}^{rm scr}(T)-M_{xi}^{rm pole}(T)$ is pretty good when $xi$ and $xi$ are scalar mesons, and show that the relation $M_{xi}^{rm scr}(T)/M_{xi}^{rm scr}(T) approx M_{xi}^{rm pole}(T)/M_{xi}^{rm pole}(T)$ is well satisfied within 20% error when $xi$ and $xi$ are pseudoscalar mesons and also when $xi$ and $xi$ are scalar mesons.
We first extend our formulation for the calculation of $pi$- and $sigma$-meson screening masses to the case of finite chemical potential $mu$. We then consider the imaginary-$mu$ approach, which is an extrapolation method from imaginary chemical pote ntial ($mu=i mu_{rm I}$) to real one ($mu=mu_{rm R}$). The feasibility of the method is discussed based on the entanglement Polyakov-loop extended Nambu--Jona-Lasinio (EPNJL) model in 2-flavor system. As an example, we investigate how reliable the imaginary-$mu$ approach is for $pi$- and $sigma$-meson screening masses, comparing screening masses at $mu_{rm R}$ in the method with those calculated directly at $mu_{rm R}$. We finally propose the new extrapolation method and confirm its efficiency.
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