Static cosmic strings in Brans-Dicke theory

Abstract

The gravitational fields of both local and global static cosmic strings in the context of Brans-Dicke theory are investigated. It is shown that, for a local cosmic string, Vilenkin's prescription for the energy-momentum tensor due to the string is inconsistent with the Brans-Dicke theory. For the global string, two kinds of solutions for the spacetime outside the string core have been presented, one of which is given in a closed form and may be nonsingular at a finite distance from the string core while the other one cannot be written in a closed form and moreover contains a singularity at a finite distance from the string core. The motions of photons and timelike particles in the field of the global string are also investigated in one of the cases. It has been shown that such a global cosmic string has only a repulsive gravitational effect on a freely moving particle.