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Register a new userViscous coefficients and thermal conductivity of a $pi K N$ gas mixture in the medium
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The temperature and density dependence of the relaxation times, thermal conductivity, shear viscosity and bulk viscosity for a hot and dense gas consisting of pions, kaons and nucleons have been evaluated in the kinetic theory approach. The in-medium cross-sections for $pipi$, $pi K$ and $pi N$ scatterings were obtained by using complete propagators for the exchanged $rho$, $sigma$, $K^*$ and $Delta$ excitations derived using thermal field theoretic techniques. Notable deviations can be observed in the temperature dependence of $eta$, $zeta$ and $lambda$ when compared with corresponding calculations using vacuum cross-sections usually employed in the literature. The value of the specific shear viscosity $eta/s$ is found to be in agreement with available estimates.
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We estimate the shear and the bulk viscous coefficients for a hot hadronic gas mixture constituting of pions and nucleons. The viscosities are evaluated in the relativistic kinetic theory approach by solving the transport equation in the relaxation time approximation for binary collisions ($pipi$,$pi N$ and $NN$). Instead of vacuum cross-sections usually used in the literature we employ in-medium scattering amplitudes in the estimation of the relaxation times. The modified cross-sections for $pipi$ and $pi N$ scattering are obtained using one-loop modified thermal propagators for $rho$, $sigma$ and $Delta$ in the scattering amplitudes which are calculated using effective interactions. The resulting suppression of the cross sections at finite temperature and baryon density is observed to significantly affect the $T$ and $mu_N$ dependence of the viscosities of the system.
The relativistic kinetic theory approach has been employed to study four well-known transport coefficients that characterize heat flow and diffusion for the case of a hot mixture constituting of nucleons and pions. Medium effects on the cross-section for binary collisions ($Npi$,$pipi$) have been taken into consideration by incorporating self-energy corrections to modify the propagator of the exchanged $Delta$ baryon in $Npi$ interaction and the $rho$ and $sigma$ meson propagators for the case of $pipi$ interaction. The temperature dependence of the four coefficients have been investigated for several values of the baryon chemical potential.
We calculate formation spectra of eta-nucleus systems in (pi,N) reactions with nuclear targets, which can be performed at existing and/or forthcoming facilities, including J-PARC, in order to investigate eta-nucleus interactions. Based on the N^*(1535) dominance in the eta N system, eta-mesic nuclei are suitable systems for study of in-medium properties of the N^*(1535) baryon resonance, such as reduction of the mass difference of N and N^* in nuclear medium, which affects level structure of the eta and N^*-hole modes. We find that clear information on the in-medium N^*- and eta-nucleus interactions can be obtained through the formation spectra of the eta-mesic nuclei. We also discuss the experimental feasibilities by showing several spectra of (pi,N) reactions calculated with possible experimental settings. Coincident measurements of pi N pairs from the N^* decays in nuclei help us to reduce backgrounds.
The appearance of some papers dealing with the $K^- d to pi Sigma n$ reaction, with some discrepancies in the results and a proposal to measure the reaction at forward $n$ angles at J-PARC justifies to retake the theoretical study with high precision to make accurate predictions for the experiment and extract from there the relevant physical information. We do this in the present paper showing results using the Watson approach and the truncated Faddeev approach. We argue that the Watson approach is more suitable to study the reaction because it takes into account the potential energy of the nucleons forming the deuteron, which is neglected in the truncated Faddeev approach. Predictions for the experiment are done as well as spectra with the integrated neutron angle.
We review the recent results of heavy meson diffusion in thermal hadronic matter. The interactions of D and B-bar mesons with other hadrons (light mesons and baryons) are extracted from effective field theories based on chiral and heavy-quark symmetries. When these guiding principles are combined with exact unitarity, physical values of the cross sections are obtained. These cross sections (which contain resonant contributions) are used to calculate the drag and diffusion coefficients of heavy mesons immersed in a thermal and dense medium. The transport coefficients are computed using a Fokker-Planck reduction of the Boltzmann equation.
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