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E. R. Bezerra de Mello

Publications and source records attributed to E. R. Bezerra de Mello.

At least 127 records · Page 7Linked to original sources
arXiv2006

Vacuum polarization by a composite topological defect

In this paper we analyze one-loop quantum effects of a scalar field induced by a composite topological defect consisting a cosmic string on a p-dimensional brane and a (m+1)-dimensional global monopole in the transverse extra dimensions. The corresponding Green function is presented as a sum of two terms. The first one corresponds to the bulk where the cosmic string is absent and the second one is induced by the presence of the string. For the points away from the cores of the topological defects the latter is finite in the coincidence limit and is used for the evaluation of the vacuum expectation values of the field square and energy-momentum tensor.

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arXiv2006

Exact Solutions of the Klein-Gordon Equation in the Presence of a Dyon, Magnetic Flux and Scalar Potential in the Specetime of Gravitational Defects

In this paper we analyse the relativistic quantum motion of a charged spin-0 particle in the presence of a dyon, Aharonov-Bohm magnetic field and scalar potential, in the spacetimes produced by an idealized cosmic string and global monopole. In order to develop this analysis, we assume that the dyon and the Aharonov-Bohm magnetic field are superposed to both gravitational defects. Two distinct configurations for the scalar potential, $S(r)$, are considered: $i)$ the potential proportional to the inverse of the radial distance, i.e., $S\propto1/r$, and $ii)$ the potential proportional to this distance, i.e., $S\propto r$. For both cases the center of the potentials coincide with the dyon's position. In the case of the cosmic string the Aharonov-Bohm magnetic field is considered along the defect, and for the global monopole this magnetic field pierces the defect. The energy spectra are computed for both cases and explicitly shown their dependence on the electrostatic and scalar coupling constants. Also we analyse scattering states of the Klein-Gordon equations, and show how the phase shifts depend on the geometry of the spacetime and on the coupling constants parameter.

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arXiv2006

Spinor Casimir effect for concentric spherical shells in the global monopole spacetime

In this paper we investigate the vacuum polarization effects associated with a massive fermionic field due to the non-trivial topology of the global monopole spacetime and boundary conditions imposed on this field. Specifically we investigate the vacuum expectation values of the energy-momentum tensor and fermionic condensate admitting that the field obeys the MIT bag boundary condition on two concentric spherical shells. In order to develop this analysis, we use the generalized Abel-Plana summation, which allows to extract from the vacuum expectation values the contribution coming from a single sphere geometry and to present the second sphere induced part in terms of exponentially convergent integrals. In the limit of strong gravitational field corresponding to small values of the parameter describing the solid angle deficit in global monopole geometry, the interference part in the expectation values are exponentially suppressed. The vacuum forces acting on spheres are presented as the sum of self-action and interaction terms. Due to the surface divergences, the first one is divergent and needs additional renormalization, while the second one is finite for all non-zero distances between the spheres. By making use of zeta function renormalization technique, the total Casimir energy is evaluated in the region between two spheres. It is shown that the interaction part of the vacuum energy is negative and the interaction forces between the spheres are attractive. Asymptotic expressions are derived in various limiting cases. As a special case we discuss the fermionic vacuum densities for two spherical shells on background of the Minkowski spacetime.

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arXiv2006

Vacuum polarization induced by a cylindrical boundary in the cosmic string spacetime

In this paper we investigate the Wightman function, the renormalized vacuum expectation values of the field square, and the energy-momentum tensor for a massive scalar field with general curvature coupling inside and outside of a cylindrical shell in the generalized spacetime of straight cosmic string. For the general case of Robin boundary condition, by using the generalized Abel-Plana formula, the vacuum expectation values are presented in the form of the sum of boundary-free and boundary-induced parts. The asymptotic behavior of the vacuum expectation values of the field square, energy density and stresses are investigated in various limiting cases. The generalization of the results to the exterior region is given for a general cylindrically symmetric static model of the string core with finite support.

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arXiv2006

Vacuum Polarization Effects on Flat Branes due to a Global Monopole

In this paper we analyse the vacuum polarization effects associated with a massless scalar field in the higher-dimensional spacetime. Specifically we calculate the renormalized vacuum expectation value of the square of the field, $<Φ^2(x)>_{Ren}$, induced by a global monopole in the "braneworld" scenario. In this context the global monopole lives in a $n=3$ dimensional sub-manifold of the higher-dimensional (bulk) spacetime, and our Universe is represented by a transverse flat $(p-1)-$ dimensional brane. In order to develop this analysis we calculate the general Green function admitting that the scalar field propagates in the bulk. Also a general curvature coupling parameter between the field and the geometry is assumed. We explicitly show that the vacuum polarization effects depend crucially on the values attributed to $p$. We also investigate the general structure of the renormalized vacuum expectation value of the energy-momentum tensor, $ _{Ren.}$, for $p=3$.

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arXiv2005

The Euclidean Scalar Green Function in the Five-Dimensional Kaluza-Klein Magnetic Monopole Spacetime

In this paper we present, in a integral form, the Euclidean Green function associated with a massless scalar field in the five-dimensional Kaluza-Klein magnetic monopole superposed to a global monopole, admitting a non-trivial coupling between the field with the geometry. This Green function is expressed as the sum of two contributions: the first one related with uncharged component of the field, is similar to the Green function associated with a scalar field in a four dimensional global monopole spacetime. The second contains the information of all the other components. Using this Green function it is possible to study the vacuum polarization effects on this spacetime. Explicitly we calculate the renormalized vacuum expectation value $<Φ^*(x)Φ(x)>_{Ren}$, which by its turn is also expressed as the sum of two contributions.

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arXiv2005

Comment to "Fine structure constant in the spacetime of a cosmic string"

In the paper Phys. Lett. B614 (2005), 140-142, F. Nasseri shows that the values of the fine structure constant reduces due to the presence of a cosmic string. In this comment I want to point out that this conclusion is not completely correct in the sense that the result obtained is valid only in a very special situation.

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arXiv2005

Casimir Densities for a Massive Fermionic Quantum Field in a Global Monopole Background with Spherical Boundary

We investigate the vacuum expectation value of the energy-momentum tensor associated with a massive fermionic field obeying the MIT bag boundary condition on a spherical shell in the global monopole spacetime. The asymptotic behavior of the vacuum densities is investigated near the sphere center and surface, and at large distances from the sphere. In the limit of strong gravitational field corresponding to small values of the parameter describing the solid angle deficit in global monopole geometry, the sphere-induced expectation values are exponentially suppressed.

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arXiv2005

Vacuum Polarization of a Massless Scalar Field in the Background of a Global Monopole with Finite Core

In this paper we analyze the vacuum polarization effects of a massless scalar field in the background of a global monopole considering a inner structure to it. Specifically we investigate the effect of its structure on the vacuum expectation value of the square of the field operator, $<\hatΦ^2(x)>$, admitting a non-minimal coupling between the field with the geometry: $ξ{\cal{R}}\hatΦ^2$. Also we calculate the corrections on the vacuum expectation value of the energy-momentum tensor, $<\hat{T}_{μν}>$, due to the inner structure of the monopole. In order to develop these analysis, we calculate the Euclidean Green function associated with the system for points in the region outside the core. As we shall see, for specific value of the coupling parameter $ξ$, the corrections caused by the inner structure of the monopole can provide relevant contributions on these vacuum polarizations.

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arXiv2005

Nonrelativistic Quantum Analysis of the Charged Particle-Dyon System on a Conical Spacetime

In this paper we develop the nonrelativistic quantum analysis of the charged particle-dyon system in the spacetime produced by an idealized cosmic string. In order to do that, we assume that the dyon is superposed to the cosmic string. Considering this peculiar configuration {\it conical} monopole harmonics are constructed, which are a generalizations of previous monopole harmonics obtained by Wu and Yang(1976 {\it Nucl. Phys. B} {\bf 107} 365) defined on a conical three-geometry. Bound and scattering wave functions are explicitly derived. As to bound states, we present the energy spectrum of the system, and analyze how the presence of the topological defect modifies obtained result. We also analyze this system admitting the presence of an extra isotropic harmonic potential acting on the particle. We show that the presence of this potential produces significant changes in the energy spectrum of the system.

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arXiv2003

Kaluza-Klein Magnetic Monopole in Five-Dimensional Global Monopole Sapcetime

In this paper we present a solution for Kaluza-Klein magnetic monopole in a five-dimensional global monopole spacetime. This new solution is a generalization of previous ones obtained by D. Gross and M. Perry (Nucl. Phys. B {\bf 226}, 29 (1983)) containing a magnetic monopole in a Ricci-flat formalism, and by A. Banerjee, S. Charttejee and A. See (Class. Quantum Grav. {\bf 13}, 3141 (1996)) for a global monopole in a five-dimensional spacetime, setting zero specific integration constant. Also we analyse the classical motion of a massive charged test particle on this manifold and present the equation for classical trajectory obeyed by this particle.

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arXiv2003

Vacuum Polarization of a Charged Massless Fermionic Field by a Magnetic Flux in the Cosmic String Spacetime

We calculate the vacuum averages of the energy-momentum tensor associated with a massless left-handed spinor fields due to magnetic fluxes on idealized cosmic string spacetime. In this analysis three distinct configurations of magnetic fields are considered: {\it{i)}} a homogeneous field inside the tube, {\it{ii)}} a magnetic field proportional to $1/r$ and {\it{iii)}} a cylindrical shell with $δ$-function. In these three cases the axis of the infinitely long tubes of radius $R$ coincides with the cosmic string. In order to proceed with these calculations we explicitly obtain the Euclidean Feynman propagators associated with these physical systems. As we shall see, these propagators possess two distinct parts. The first are the standard ones, i.e., corresponding to the spinor Green functions associated with the massless fermionic fields on the idealized cosmic string spacetime with a magnetic flux running through the line singularity. The second parts are new, they are due to the finite thickness of the radius of the tubes. As we shall see these extra parts provide relevant contributions to the vacuum averages of the energy-momentum tensor.

hep-th↗
arXiv2003

Spinor Casimir densities for a spherical shell in the global monopole spacetime

We investigate the vacuum expectation values of the energy-momentum tensor and the fermionic condensate associated with a massive spinor field obeying the MIT bag boundary condition on a spherical shell in the global monopole spacetime. In order to do that it was used the generalized Abel-Plana summation formula. As we shall see, this procedure allows to extract from the vacuum expectation values the contribution coming from to the unbounded spacetime and explicitly to present the boundary induced parts. As to the boundary induced contribution, two distinct situations are examined: the vacuum average effect inside and outside the spherical shell. The asymptotic behavior of the vacuum densities is investigated near the sphere center and surface, and at large distances from the sphere. In the limit of strong gravitational field corresponding to small values of the parameter describing the solid angle deficit in global monopole geometry, the sphere-induced expectation values are exponentially suppressed. As a special case we discuss the fermionic vacuum densities for the spherical shell on background of the Minkowski spacetime. Previous approaches to this problem within the framework of the QCD bag models have been global and our calculation is a local extension of these contributions.

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arXiv2003

Vacuum Polarization by a Magnetic Flux in a Cosmic String Background

In this paper we analyse the vacuum polarization effects due to a magnetic flux on massless fermionic fields in a cosmic string background. Three distinct configurations of magnetic fields are considered. In all of them the magnetic fluxes are confined in a long cylindrical tube of finite radius.

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arXiv2003

Vacuum Polarization of a Charged Massless Scalar Field on Cosmic String Spacetime in the Presence of a Magnetic Field

In this paper we consider a charged massless scalar quantum field operator in the spacetime of an idealized cosmic string, i.e., an infinitely long, straight and static cosmic string, which presents a magnetic field confined in a cylindrical tube of finite radius. Three distinct situations are taking into account in this analysis: {\it{i)}} a homogeneous field inside the tube, {\it{ii)}} a magnetic field proportional to $1/r$ and {\it{iii)}} a cylindrical shell with $δ$-function. In these three cases the axis of the infinitely long tube of radius $R$ coincides with the cosmic string. In order to study the vacuum polarization effects outside the tube, we explicitly calculate the Euclidean Green function associated with this system for the three above situations, considering points in the region outside the tube.

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arXiv2003

Nonrelativistic Scattering Analysis of Charged Particle by a Magnetic Monopole in the Global Monopole Background

We analyze the nonrelativistic quantum scattering problem of a charged particle by an Abelian magnetic monopole in the background of a global monopole. In addition to the magnetic and geometric effects, we consider the influence of the electrostatic self-interaction on the charged particle. Moreover, for the specific case where the electrostatic self-interaction becomes attractive, charged particle-monopole bound system can be formed and the respective energy spectrum is hydrogen-like one.

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