2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/200426Different models of the cosmic substratum which pretend to describe the present stage of accelerated expansion of the Universe like the $Λ$CDM model or a Chaplygin gas, can be seen as special realizations of a holographic dark energy cosmology if the option of an interaction between pressurless dark matter and dark energy is taken seriously. The corresponding interaction strength parameter plays the role of a cosmological constant. Differences occur at the perturbative level. In particular, the pressure perturbations are intrinsically non-adiabatic.9 pages, selected for "Honorable Mention" by the Gravity Research FoundationGeneral Relativity and Quantum CosmologyAstrophysicsHigh Energy Physics - Theorytext