In an Euclidean space with a conical-type line singularity, we determine the Green's function for a charged massive scalar field interacting with a magnetic flux running through the line singularity. We give an integral expression of the Green's function and a local form in the neighbourhood of the point source, where it is the sum of the usual Green's function in Euclidean space and a regular term. As an application, we derive the vacuum energy-momentum tensor in the massless case for an arbitrary magnetic flux.

In this paper we analyze the gravitational field of a global monopole in the context of f (R) gravity. More precisely, we show that the field equations obtained are expressed in terms of F (R) = df (R) dR . Since we are dealing with a spherically symmetric system, we assume that F (R) is a function of the radial coordinate only. Moreover, adopting the weak field approximation, we can provide all components of the metric tensor. A comparison with the corresponding results obtained in General Relativity and in the Brans-Dicke theory is also made.

In this paper we suggest an approach to analyse

The gravitational properties of a local cosmic string in the framework of scalar-tensor gravity are examined. We find the metric in the weak-field approximation and we show that, contrary to the General Relativity case, the cosmic string in scalar-tensor gravitation exerces a force on non-relativistic, neutral test particle. This force is propor-*

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...

We study the modifications on the metric of an isolated self-gravitating bosonic superconducting cosmic string in a scalar-tensor gravity in the weak-field approximation. These modifications are induced by an arbitrary coupling of a massless scalar field to the usual tensorial field *

The authors determine some gravitational effects in the classical and quantum massive scalar field theories near a point mass in the Einstein theory in three dimensions and near a particular spinning point mass in the topologically massive gravity. Classically, they find the expression, to a first-order approximation in the deficit angle of the conical spacetime, for the self-force acting on a scalar charge at rest. Within quantum field theory, they obtain the vacuum expectation value of the energy-momentum operator for a massive scalar field by determining the Euclidean Green function. They provide an explicit expression for the vacuum energy-momentum tensor to first order in the deficit angle for an arbitrary coupling parameter. Near a point mass in the Einstein theory, they calculate the gravitational force on a massive test particle due to the backreaction of the vacuum energy-momentum tensor. For the minimal and conformal couplings, they show that the gravitational force is always attractive. Near the particular spinning point mass in the topologically massive gravity, they can prove that the gravitational force is always attractive for a massless scalar field.

The viability of achieving gravitational consistent braneworld models in the framework of a f (R) theory of gravity is investigated. After a careful generalization of the usual junction conditions encompassing the embedding of the 3-brane into a f (R) bulk, we provide a prescription giving the necessary constraints in order to implement the projected second order effective field equations on the brane.