Dynamical constraints on variable vacuum energy in Brans-Dicke theory

Abstract

In this research work, we investigate the late-time accelerated expansion of the universe within the framework of Brans-Dicke theory by considering dynamical vacuum energy models with a time-varying cosmological constant. Two vacuum energy models are studied, namely the hybrid vacuum law $\Lambda(t)=\alpha H^{2}+\beta\dot{H}$ and the power vacuum law $\Lambda(H)=\alpha_{1}H^{n}$, where $\alpha$, $\beta$, $\alpha_{1}$ and $n$ are free parameters. We derive analytical solutions for the Hubble parameter and other relevant cosmological quantities. The evolution of the deceleration parameter, the effective equation of state parameter, the cosmographic parameters, the behaviour of Om($\mathit{z}$) diagnostics and the present age of the universe are examined. Furthermore, the analysis of the $\omega_{\rm eff}-\omega'_{\rm eff}$ plane shows that the model evolves in the freezing region and the thermodynamic analysis confirms that the generalized second law of thermodynamics is satisfied within the power vacuum law model.