Brans–Dicke cosmology with cosmological term [formula omitted

Abstract

In this paper, we study the dynamics of a flat Friedmann–Lemaître–Robertson–Walker (FLRW) cosmological model by considering varying vacuum energy density (VED) in Brans–Dicke (BD) cosmology. For this purpose, we consider the well-motivated VED of the form Λ(H)=c0+3νH2, where c0 and ν are dimensionless constants. We first adopt a theoretical method to find the exact solutions for various cosmological parameters of two models, namely ΛRG1 and ΛRG2. In ΛRG1 model, the scale factor evolves as a power-law expansion which gives the deceleration parameter a constant value. Hence, this type of model does not show the transition phase. The second model ΛRG2 describes the transition phase from deceleration to acceleration. In the second part, we perform two joint likelihood analysis in order to find the constrain on the main free parameters of the ΛRG2 model using the latest observational data sets including SNe Pantheon, H(z) data, BAO/CMB data and local H0 by SH0ES. Performing the two different combination of datasets, we find that the model shows prior decelerated epoch followed by late time accelerated epoch. We also compare the decaying VED with traditional Λ cosmology, which help us to define the evolution of the VED model. The results show that varying VED model in BD theory is consistent with data and the cosmic evolutions are in good agreement with the concordance ΛCDM and BD with constant Λ models. The AIC and BIC selection criteria are also discussed.