$\sigma$CDM coupled to radiation. Dark energy and Universe acceleration

TL;DR

This paper extends the $\sigma$CDM cosmological model to include radiation and explores how varying the interaction parameter affects the universe's acceleration, using MCMC to constrain initial conditions and compare with $\Lambda$CDM.

Contribution

It introduces an extension of the $\sigma$CDM model to earlier cosmic times and analyzes the impact of the interaction parameter on cosmic acceleration.

Findings

Certain coupling constants prevent transition to accelerated expansion.

The model's parameters are constrained by current dark matter, dark energy, and radiation measurements.

Comparison with $\Lambda$CDM shows both similarities and differences in evolution.

Abstract

Recently the Chiral Cosmological Model (CCM) coupled to cold dark matter (CDM) has been investigated as $\sigma$CDM model to study the observed accelerated expansion of the Universe. Dark sector fields (as Dark Energy content) coupled to cosmic dust were considered as the source of Einstein gravity in Friedmann-Robertson-Walker (FRW) cosmology. Such model had a beginning at the matter-dominated era. The purposes of our present investigation are two folds: to extend <<life>> of the $\sigma$CDM for earlier times to radiation-dominated era and to take into account variation of the exponential potential via variation of the interaction parameter $\lambda $. We use Markov Chain Monte Carlo (MCMC) procedure to investigate possible values of initial conditions constrained by the measured amount of the dark matter, dark energy and radiation component today. Our analysis includes dark energy contribution to critical density, the ratio of the kinetic and potential energies, deceleration parameter, effective equation of state and evolution of DE equation of state with variation of coupling constant $\lambda $. A comparison with the $\Lambda$CDM model was performed. A new feature of the model is the existence of some values of potential coupling constant, leading to a $\sigma$CDM solution without transit into accelerated expansion epoch.