Anisotropic Cosmological Model in Brans-Dicke Theory of Gravitation

In this paper, we study an anisotropic cosmological model in scalar tensor theory of gravitation proposed by Brans-Dicke, considering a Bianchi type- spacetime geometry filled with a macroscopic body. To solve the nonlinear Brans-Dicke field equations by using the average scale factor and the relation between metric coefficients, with a radiation universe, we obtained exact solutions for the metric functions and scalar field. We derive and analyze several key cosmological parameters as functions of redshift, including the Hubble parameter, expansion scalar, shear scalar, energy density, pressure and the Brans-Dicke scalar field. The evolution of these parameters is graphically illustrated, revealing that the model predicts an expanding universe with dynamics transitioning from an early decelerating phase to a late-time acceleration. The behavior of the deceleration parameter supports the accelerated expansion in accordance with current observational data. Furthermore, we investigate higher-order cosmological diagnostics such as the jerk and snap parameters as well as the statefinder parameters which are instrumental in distinguishing this model from the standard cosmology and other dark energy models. We also explore the Om diagnostic to characterize dark energy evolution and compare our theoretical Hubble parameter values with a compilation of 57 recent Hubble dataset points obtained from differential age (DA) and baryonic acoustic oscillation (BAO) methods. A good agreement is observed between the model predictions and observational data, as indicated by the best-fit curve with minimal root mean square error.