Descripción: We introduce an effective one-uid description of the interacting dark sector in a spatially at Friedmann-Robertson-Walker space-time and investigate the stability of the power-law solutions. We find the "source equation" for the total energy density and determine the energy density of each dark component. We study linear and nonlinear interactions which depend on the dark matter and dark energy densities, their first derivatives, the total energy density with its derivatives up to second order and the scale factor. We solve the evolution equations of the dark components for both interactions, examine exhaustively several examples and show cases where the problem of the coincidence is alleviated. We show that a generic nonlinear interaction gives rise to the "relaxed Chaplygin gas model" whose effective equation of state includes the variable modified Chaplygin gas model while some others nonlinear interactions yield de Sitter and power-law scenarios. © 2012 American Institute of Physics.

Descripción: We extend the homogeneous modified Chaplygin cosmologies to large-scale perturbations by formulating a Zeldovich-like approximation. We show that the model interpolates between an epoch with a soft equation of state and a de Sitter phase, and that in the intermediate regime its matter content is simply the sum of dust and a cosmological constant. We then study how the large-scale inhomogeneities evolve and compare the results with cold dark matter (CDM), ΛCDM and generalized Chaplygin scenarios. We find that unlike that like the latter, our models resemble ΛCDM. © 2005 Elsevier B.V. All rights reserved.

Descripción: We examine a spatially flat Friedmann-Robertson-Walker (FRW) universe filled with interacting dark matter and a modified holographic Ricci dark energy (MHRDE). The interaction term is selected as a significant rational function of the total energy density and its first derivative homogeneous of degree. We show that the effective one-fluid obeys the equation of state of a relaxed Chaplygin gas, then the universe turns to be dominated by pressureless dark matter at early times and undergoes an accelerated expansion in the far future driven by a strong negative pressure. Performing a X2-statistical analysis with the observational Hubble data and the Union2 compilation of SNe Ia, we place some constraints on cosmological parameters analyzing the feasibleness of the modified holographic Ricci ansatz. It turned that MHRDE gets the accelerated expansion faster than the ΛCDM model. Finally, a new model with a component that does not exchange energy with the interacting dark sector is presented for studying bounds on the dark energy at early times. © 2012 American Institute of Physics.