Spherically symmetric thin shells in Brans-Dicke theory of gravity.

Abstract

The dynamics of spherically symmetric thin shells (or bubbles) is studied in the framework of the Brans-Dicke theory of gravity, using the Newman-Penrose formalism. The Brans-Dicke (BD) gravitational field equations on the bubble wall are given explicitly in terms of the discontinuities of the metric coefficients and the BD scalar field. Consequently, once the space-time geometry outside of the wall is given, these equations, together with the equation of state of the wall, uniquely determine the motion of the bubble. Using the ``generalized'' Bianchi identities, the interaction of a bubble with gravitational and matter fields is investigated. In particular, it is found that a bubble does not interact with an electromagnetic field, but it does with a scalar field or a fluid. The attraction and repulsion of a bubble are also studied. Exact solutions are constructed, and it is found that some of these solutions represent wormholes. However, these wormholes are different from the ones in Einstein's theory of gravity, in the sense that the throats of the wormholes are not necessarily built with ``exotic'' matter.