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Description
The shear viscosity is calculated microscopically via
the Green-Kubo relation in the various snapshots in the central region
in an ongoing relativistic collision simulated via the UrQMD framework
for various bombarding energies in the anticipated NICA experiments.
In previous works the shear
viscosity was calculated as function of temperature, while the chemical
potential of baryon charge was kept constant. The original idea of this work
is to extract, in various time windows, the average energy
density, the net baryon density and the small though nonzero net
strangeness density. By fitting these parameters to statistical model,
we obtain temperature and chemical potentials of baryon charge
and strangeness. Simultaneously, these parameters are used to start
simulation in a box, again within the UrQMD transport model. From these
simulations the autocorrelations in time of the energy stress tensor
are extracted, and subsequently via the Green-Kubo identities the
shear viscosity coefficient of that equilibrium hadronic system is
obtained. Finally, the
evolving and decreasing shear viscosity coefficient can be given as a
function of time, temperature, and chemical potentials in the center of
mass of the system. For all four collision energies from 10A GeV to
40A GeV a shear viscosity to entropy ratio ($\eta/S$) typically starts from
0.3 and then rapidly increases up to and even larger than 1.
In addition, we calculate also partial viscosity both for nucleons and pions.
References:
[1] M. Teslyk, L. Bravina, O. Panova, O. Vitiuk, E. Zabrodin, Phys. Rev. C 101 (2020) 014904
[2] E. Zabrodin, M. Teslyk, O. Vitiuk, L. Bravina, Phys. Scr. 95 (2020) 074009
