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In the last decades, several observations have pointed out that the Universe is in an ongoing period of accelerated expansion that is driven by the presence of an exotic fluid with negative pressure. Its simplest form is a cosmological constant Λ, having an equation of state w=−1. More complicated prescriptions lead to the so-called Dark Energy (DE). Although several models have been proposed to explain DE, the observations have only determined that it accounts for ∼68% of the total energy-density budget of the Universe, while its fundamental nature is still unknown. In addition, we should mention that the accelerated expansion of the Universe could also be explained by several modifications of the gravitational action. For example, introducing higher order terms of the Ricci curvature in the Hilbert–Einstein Lagrangian gives rise to effective matter stress-energy tensor which could drive the current accelerated expansion. Another alternative for reproducing the dark energy effects is by introducing non-derivative terms interactions in the action, in addition to the Einstein-Hilbert action term, such that it creates the effect of a massive graviton.
Decaying Dark Energy
We were interested in exploring a specific decaying DE model, leading to the creation/annihilation of photons and Dark Matter (DM) particles. Since DE continuously decays into photons and/or DM particles along with the cosmic evolution, the relation between the temperature of the Cosmic Microwave Background (CMB) radiation and the redshift is modified. We adopted the following functional law for DE:
We used the most recent observationally-determined datasets, including Supernovae Type Ia and Gamma-Ray Bursts data, along with H(z) and Cosmic Microwave Background temperature versus z data and the reduced Cosmic Microwave Background parameters, to improve the previous constraints on these models.
Our results suggested that the accelerated expansion of the Universe is well described by the cosmological constant, and we argued that forthcoming observations will play a determinant role to constrain/rule out decaying Dark Energy [1].
Bibliography:
Ivan De Martino, ’Decaying dark energy in light of the latest cosmological dataset.’, 2018, Symmetry, 10, 372
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