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

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 Added by Masahiro Ishii
 Publication date 2015
  fields
and research's language is English




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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 potential ($mu=i mu_{rm I}$) 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.
In this work, we carried out quantum many-body studies of magnetic monopole ensembles through numerical simulations of the path integral for one- and two-component Coulomb Bose systems. We found the relation between the critical temperature for the Bose-Einstein condensation phase transition and the Coulomb coupling strength using two methods, the finite-size scaling of the superfluid fraction and statistical analysis of permutation cycles. After finding parameters that match the correlation functions measured in our system with the correlation functions previously measured on the lattice, we arrived at an effective quantum model of color magnetic monopoles in QCD. From this matched model, we were able to extract the monopole contribution to QCD equation of state near $T_text{c}$.
We incorporate the effective restoration of $U(1)_{rm A}$ symmetry in the 2+1 flavor entanglement Polyakov-loop extended Nambu--Jona-Lasinio (EPNJL) model by introducing a temperature-dependent strength $K(T)$ to the Kobayashi-Maskawa-t Hooft (KMT) determinant interaction. $T$ dependence of $K(T)$ is well determined from pion and $a_0$-meson screening masses obtained by lattice QCD (LQCD) simulations with improved p4 staggered fermions. The strength is strongly suppressed in the vicinity of the pseudocritical temperature of chiral transition. The EPNJL model with the $K(T)$ well reproduces meson susceptibilities calculated by LQCD with domain-wall fermions. The model shows that the chiral transition is second order at the light-quark chiral-limit point where the light quark mass is zero and the strange quark mass is fixed at the physical value. This indicates that there exists a tricritical point. Hence the location is estimated.
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