Varying Cosmological Constant and the Machian Solution in the Generalized Scalar-Tensor Theory

Abstract

The cosmological constant $(1/2)\lambda_{1}\phi_{, \mu}\phi ^{, \mu}/\phi ^{2}$ is introduced to the generalized scalar-tensor theory of gravitation with the coupling function $\omega (\phi)=\eta /(\xi -2)$ and the Machian cosmological solution satisfying $\phi =O(\rho /\omega)$ is discussed for the homogeneous and isotropic universe with a perfect fluid (with negative pressure). We require the closed model and the negative coupling function for the attractive gravitational force. The constraint $% \omega (\phi)<-3/2$ for $0\leqq \xi <2$ leads to $\eta >3$. If $\lambda_{1}<0$ and $0\leqq -\eta /\lambda_{1}<2$, the universe shows the slowly accelerating expansion. The coupling function diverges to $-\infty $ and the scalar field $\phi $ converges to $G_{\infty}^{-1}$ when $\xi \to 2$ ($t\to +\infty $). The cosmological constant decays in proportion to $t^{-2}$. Thus the Machian cosmological model approaches to the Friedmann universe in general relativity with $\ddot{a}=0$, $\lambda =0$, and $p=-\rho /3$ as $t\to +\infty $. General relativity is locally valid enough at present.