Composite vacuum Brans-Dicke wormholes

Abstract

We construct a new static spherically symmetric configuration composed of interior and exterior Brans-Dicke vacua matched at a thin matter shell. Both vacua correspond to the same Brans-Dicke coupling parameter $\omega$, however they are described by the Brans class I solution with different sets of parameters of integration. In particular, the exterior vacuum solution has $C_{ext}(\omega)\equiv 0$. In this case the Brans class I solution for any $\omega$ reduces to the Schwarzschild one being consistent with restrictions on the post-Newtonian parameters following from recent Cassini data. The interior region possesses a strong gravitational field, and so the interior vacuum solution has $C_{int}(\omega)=-1/(\omega+2)$. In this case the Brans class I solution describes a wormhole spacetime provided $\omega$ lies in the narrow interval $-2-\frac{\sqrt{3}}{3}<\omega<-2$. The interior and exterior regions are matched at a thin shell made from an ordinary perfect fluid with positive energy density and pressure obeying the barotropic equation of state $p=k\sigma$ with $0\le k\le1$. The resulting configuration represents a composite wormhole, i.e. the thin matter shell with the Schwarzschild-like exterior region and the interior region containing the wormhole throat.