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Abstract
Recently, a new cosmological framework, dubbed Ricci cosmology, has been proposed. Such a framework has emerged from the study of relativistic dynamics of fluids out of equilibrium in a curved background and is characterised by the presence of deviations from the equilibrium pressure in the energy–momentum tensor which are due to linear terms in the Ricci scalar and the Ricci tensor. The coefficients in front of such terms are called the second order transport coefficients and they parametrise the fluid response to the pressure terms arising from the spacetime curvature. Under the preliminary assumption that the second order transport coefficients are constant, we find the simplest solution of Ricci cosmology in which the presence of pressure terms causes a departure from the perfect fluid redshift scaling for matter components filling the Universe. In order to test the viability of this solution, we make four different ansätze on the transport coefficients, giving rise to four different cases of our model. On the physical ground of the second law of thermodynamics for fluids with non-equilibrium pressure, we find some theoretical bounds (priors) on the parameters of the models. Our main concern is then the check of each of the case against the standard set of cosmological data in order to obtain the observational bounds on the second order transport coefficients. We find those bounds also realising that Ricci cosmology model is compatible with Lambda CDM cosmology for all the ansätze.
Highlights
Acoustic Oscillation (BAO) [3] and Cosmic Microwave Background (CMB) anisotropies [4], have pointed in the same direction making the explanation of these observations so compelling that it has become one of the central issues of modern cosmology.The most successful model in explaining such feature of our Universe and in fitting the available data (SnIa, Baryon Acoustic Oscillations (BAO), CMB, Big Bang Nucleosynthesis (BBN) and Large Scale Structure (LSS)) is the Standard Cosmological Model, better known as Cold Dark Matter (CDM) [5,6], in which the Universe is well described below the Planck scale by General Relativity (GR) and at scales of 100 Mpc and larger each component of the Universe can be described as a perfect fluid
The most successful model in explaining such feature of our Universe and in fitting the available data (SnIa, BAO, CMB, Big Bang Nucleosynthesis (BBN) and Large Scale Structure (LSS)) is the Standard Cosmological Model, better known as CDM [5,6], in which the Universe is well described below the Planck scale by General Relativity (GR) and at scales of 100 Mpc and larger each component of the Universe can be described as a perfect fluid
In this paper we have explored for the first time the physical consequences of the recently proposed framework of Ricci cosmology on the late time Universe
Summary
Acoustic Oscillation (BAO) [3] and Cosmic Microwave Background (CMB) anisotropies [4], have pointed in the same direction making the explanation of these observations so compelling that it has become one of the central issues of modern cosmology. The models that can describe the latetime accelerated expansion of the Universe are considered [33–46] These models have revealed to be successful in reproducing the background evolution of the Universe at late time while attempting to solve the problems of CDM, unify or replace the dark components of the Universe and be compatible with the large structure formation. It is still debated whether viscous terms in the pressure may or may not contribute to relieve the Hubble tension [47–49].
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