Narrow Results

We provide a detailed description for power-law scaling FRW cosmological models in Brans–Dicke theory dominated by two interacting fluid components during the expansion of the universe.

In this paper, we study two different dynamic structures of holographic dark energy, namely Tsallis and Kaniadakis, within the framework of Brans–Dicke cosmology. We consider the complex form of the quintessence model and examine both non-interacting and interacting cases, calculating various cosmological parameters such as the equation of state $\omega$ and discussing the behavior of $\omega -{\omega }^{\prime }$. We modify the potential and study the scalar field dynamics of complex quintessence cosmology. Additionally, we examine the effects of the two parts of the quintessence field (real and complex) and the fractional energy density ${\mathrm{\Omega }}_D$, determining whether they can describe a real universe. We note that the fractional energy density cannot be arbitrary between 0 and 1, as it depends on the Tsallis, Kaniadakis and Brans–Dicke cosmology-free parameters. For each model, we establish a relationship between the fractional energy density and other parameters such as $\delta$, $b^2$, $\alpha$ and $\beta$.

We consider the dynamics of a causal bulk viscous cosmological fluid filled flat homogeneous Universe in the framework of the Brans–Dicke theory. Three classes of exact solutions of the field equations are obtained and the behavior of the physical parameters is considered in detail. In this model the energy density associated to the Brans–Dicke scalar field is of the same order of magnitude as the matter energy density. The inclusion of the bulk viscous pressure term in the matter energy-momentum tensor leads to a non-decelerating evolution of the Universe.

In this paper, we study the effect of the quantum backreaction on Brans–Dicke cosmology in inflation era. We consider an inflaton field in the $D$-dimensional spacetime in the framework of Brans–Dicke model. We use a new notation for the Brans–Dicke field in terms of the dilaton field. Then we obtain the vacuum expectation value of the full energy–momentum tensor using WKB approximation of the mode functions which satisfy the equations of motion. The obtained vacuum expectation values of energy–momentum tensor are divergent. In order to renormalize it, we introduce a constant cut-off $\mathrm{\Omega }$. The vacuum expectation value of energy–momentum tensor is separated to the UV and IR parts by using $\mathrm{\Omega }$ cut-off. Then, we use the dimensional regularization method to eliminate divergences by introducing a counterterm action. Also, we calculate the IR contribution of the vacuum expectation value of energy–momentum tensor. Thus, we obtain a physically finite result for the quantum energy–momentum tensor. Finally, we find the effect of backreaction on scale factor.