Hidden invariance in Gurzadyan-Xue cosmological models

The dark energy formula derived by Gurzadyan and Xue which leads to a value fitting the SN data, provides a scaling relation between the physical constants and cosmological parameters and defines a set of cosmological models. In previous works we have considered several of those models and derived the cosmological equations for each case. In this letter, we present the phase portrait analysis of those models. Surprisingly we found, first, that the separatrix in the phase space which determines the character of solutions depends solely on the value of the current matter density. Namely, at $\Omega_m>2/3$ the equations describe Friedmannian Universe with the classical singularity at the beginning. While at $\Omega_m<2/3$ all solutions for all models start with zero density and non vanishing scale factor. Secondly, more remarkable, the value $\Omega_{sep}=2/3$ defining the separatrix is the same for all models, which reveales an underlying invariance hidden in the models, possibly, due to the basic nature of the GX-scaling.Comment: to appear in Physics Letters