Scalar perturbations in the late Universe: viability of the Chaplygin
  gas models
  We study the late-time evolution of the Universe where dark energy (DE) is
parametrized by a modified generalized Chaplygin gas (mGCG) on top of cold dark
matter (CDM). We also take into account the radiation content of the Universe.
In this context, the late stage of the evolution of the universe refers to the
epoch where CDM is already clustered into inhomogeneously distributed discrete
structures (galaxies, groups and clusters of galaxies). Under these conditions,
the mechanical approach is an adequate tool to study the Universe deep inside
the cell of uniformity. To be more accurate, we study scalar perturbations of
the Friedmann-Lema\^itre-Robertson-Walker metric due to inhomogeneities of CDM
as well as fluctuations of radiation and mGCG, the later driving the late-time
acceleration of the universe. Our analysis applies as well to the case where
mGCG plays the role of DM and DE. We select the sets of parameters of the mGCG
that are compatible with the mechanical approach. These sets define prospective
mGCG models. By comparing the selected sets of models with some of the latest
observational data results, we conclude that the mGCG is in tight agreement
with those observations particularly for a mGCG playing the role of DE and DM.
