One-parameter dynamical dark-energy from the generalized Chaplygin gas

The fact that Einstein's equations connect the space-time geometry to the total matter content of the cosmic substratum, but not to individual contributions of the matter species, can be translated into a degeneracy in the cosmological dark sector. Such degeneracy makes it impossible to distinguish cases where dark energy (DE) interacts with dark matter (DM) from a dynamical non-interacting scenario using observational data based only on time or distance measurements. In this paper, based on the non-adiabatic generalized Chaplygin gas (gCg) model, we derive and study some cosmological consequences of a varying one -parameter dynamical DE parameterization, which does not allow phantom crossing. We perform a parameter selection using the most recent publicly available data, such as the data from Planck 2018, eBOSS DR16, Pantheon and KiDS-1000. In light of this analysis, we assess how our model responds to the S8 tension. We find that CMB data impose strong constraints on the model and conclude that the S8 tension can be alleviated only for values of the model parameters very close to the ACDM cosmology.