Brane cosmic string compactification in Brans-Dicke theory

Abstract

We investigate an alternative compactification of extra dimensions using local cosmic string in the Brans-Dicke gravity framework. In the context of dynamical systems it is possible to show that there exist a stable field configuration for the Einstein-Brans-Dicke equations. We explore the analogies between this particular model and the Randall-Sundrum scenario. DOI: 10.1103/PhysRevD.75.084028 PACS numbers: 11.25.ÿw, 04.50.+h, 12.60.Fr The search of an alternative compactification of extra dimensions is a very interesting tool to analyze the hierarchy problem in string theory. Among other physical implications, they provide a beautiful scenario of our universe, inserting it on a brane [1,2]. In the Randall-Sundrum (RS) model there are two 3-branes in an orbifold with Z 2 symmetry in five dimensions [3]. A warp factor in the metric shows how this type of model can help us with the hierarchy problem, and beyond it, the model is a 5-D realization of Horava-Witten solution [4]. Many physical effects related to the extra dimensions can be calculated using the standard brane-world gravity [5]. However, from the point of view of topological defects, these models use global domain walls to generate the branes [6]. But cosmologists call our attention to cosmological problems related to global defect like domain walls [7]. In this vein an interesting alternative (global strings) was given in [8] that provides in six dimensions all the necessary structure; three-brane plus transverse space.On the other hand, scalar-tensorial theories, in particular, the Brans-Dicke [9], stand for many reasons as a good laboratory to develop these kinds of physical models. First, they show a robust relation with gravity coming from fundamental string theory at low energy. Second, they can be tested by experimental observations. Besides, theoretically we hope that the additional scalar field plays an important role in the distribution of masses of the fundamental particles.A particular and important characteristic of the models like RS and the one found in [8,10] is that the topological defect can compactify the spacetime around it by itself, leading to a singularity. Topological domain walls and global strings effectively do it, but if one introduces a time dependent factor on the metric in the case of a global string the solution presents a cosmological event horizon free of singularity [11]. However this event horizon is not stable [12]. In Einstein's theory only global defects have this property. However, when we look at the equations of a local cosmic string in the Brans-Dicke theory they seem to have that property, except for the fact that there is no singularity at GUT scale [13]. In other words, local cosmic string in the Brans-Dicke theory is similar, in this context, to global string in Einstein's gravity.Our effort here is to present a model of alternative compactification using a local string in the Brans-Dicke theory. In the course of development we shall use several approximations and by using a dynamical system argument we...

On the Consistency Conditions to Braneworlds in Scalar-Tensor Gravity for Arbitrary Dimensions

“…An important characteristic about braneworld models in the BD theory is that, generally, the scalar field depends only on the large extra dimensions [10]. This type of dependence is indeed useful since the projected EBD equations on the brane leads to important subtle modifications but still resembles the Einstein's equations [11].…”

“…Let us particularize our analysis to braneworld models inspired in one of those previously found in this framework. In the models proposed in [10], all the bulk-brane structure was generated by using local and global cosmic string as sources. The final scenario is composed by 4-branes…”

Global monopole as a generator of a bulk-brane structure in Brans–Dicke bulk gravity

“…In Ref. [10] a local cosmic string generating the braneworld model was studied, while in Ref. [11] a braneworld was investigated with the aid of a global cosmic string.…”

Smooth braneworld models possibility in modified gravities

“…Therefore, in order to investigate whether the no-go theorem is valid in the Brans-Dicke case, we have to adequate our previous approach to this case [13,14].…”

“…On the other hand, as stated, since the equivalence is only valid for specific cases, a full treatment of both cases is necessary. It is interesting to note that the consistency conditions were already incorporated in the context of f (R) [12] and BD gravities [13,14], in these works it was shown that both f (R) and BD theories are suitable to accommodate consistent scenarios without negative tension branes.…”