Cosmic string configuration in a five dimensional Brans-Dicke theory

We consider a scalar field interacting with a cosmic string configuration. The origin of the scalar field is given by a compactification mechanism in the context of a five-dimensional Brans-Dicke theory. We analyze the behavior of a charged cosmic string given by the Maxwell-Chern-Simons term on the 3-brane. The Cosmic Microwave Background Radiation constraint is used to analyze the possibility of optical activity effect in connection with the Brans-Dicke parameter $\ensuremath{\omega}$. We show that the dilatons produced by a cosmic string can decay into gauge bosons with masses given by the compactification modes. The Brans-Dicke parameter $\ensuremath{\omega}$ imposes stringent constraints on the mass of the dilaton and help us to understand the energy scales. In this scenario the lifetime of the dilaton which decays into light gauge bosons as well as the dependence of this phenomenon with the Brans-Dicke parameter are estimated.