Scalar field in the Jordan‐Brans‐Dicke Theory and Dark Energy

The article considers cosmological models in the framework of the Jordan‐Brans‐Dicke (JBD) theory in the Einstein frame. It separately discusses the cases of scalar field domination, as well as the presence of cosmological constant Λ, with matter, which is described by the barometric equation of state $P = αε$ (P‐pressure, ε‐energy density of matter). The analysis of obtained results is carried out in the light of modern observational data. It is shown that the contribution of the scalar field and Λ‐term (Λ>0) in the case of $q = −12(q = äaȧ2$ decelerating parameter) compensate each other, and the situation becomes like in Einstein’s theory.