Shear and Bulk Viscosities of a Hadron Gas Within Relaxation Time Approximation and its Test

  • O. N. Moroz Bogolyubov Institute for Theoretical Physics, Nat. Acad. of Sci. of Ukraine
Keywords: relaxation time approximation, bulk viscosity, shear viscosity, hadron gas

Abstract

We concentrate on the calculation of the shear and bulk viscosities of a hadron gas. They define its dissipative dynamics and influence its experimentally measurable elliptic flow. Due to the difficulty of this calculation, the relaxation time approximation (RTA) was used in previous works. As those results have approached the realistic ones, there is a need to find out how accurate RTA is. For this sake, we calculate the viscosities in RTA, by using the cross sections extracted from the ultrarelativistic quantum molecular dynamics (UrQMD) model and compare them with the same ones calculated without RTA. This allows us to find the estimates of errors due to the application of RTA in the calculations of viscosities, which are valid also for other similar models. For instance, in the temperature region 100 MeV < T < 160 MeV at zero chemical potentials, the shear viscosity becomes smaller up to 1.57 times or up to 1.45 times if the averaged relaxation time is used. This has important consequences for the interpretation of the previously made calculations of viscosities and some other related calculations. Within RTA, we also find estimation of the enhancement of the bulk viscosity of a hadron gas because of the nonconservation of particle numbers.

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Published
2018-10-11
How to Cite
Moroz, O. (2018). Shear and Bulk Viscosities of a Hadron Gas Within Relaxation Time Approximation and its Test. Ukrainian Journal of Physics, 58(12), 1127. https://doi.org/10.15407/ujpe58.12.1127
Section
Nuclei and nuclear reactions