Hubble's Law in Heavy Ion Collisions

The evolution of the "microscopic" Hubble parameter related to the expansion of matter born in heavy-ion collisions was obtained for nucleons and pions. The calculations were carried out within the parton-hadron-string dynamics (PHSD) transport model. Au+Au collisions with $\sqrt{s_{NN}} = 7.8$ GeV at $b = 2.5,\ 5.0,\ 7.5$, and $10.0$ fm were considered. A new method for determining the "microscopic" Hubble parameter from simulated data was used. The ballistic motion was obtained for the longitudinal direction after the separation of the nuclei. In earlier times, the evolution of the "microscopic" Hubble parameter in this direction was more complicated. For transverse directions, an exponential low-time asymptotics of the Hubble parameter was observed. The obtained values of the "microscopic" Hubble parameter are about 40 orders of magnitude higher than the cosmological Hubble constant.