Higher Dimensional Cosmic String Research Articles

Vacuum current and polarization induced by magnetic flux in a higher-dimensional cosmic string in the presence of a flat boundary

In this present paper, we investigate the vacuum bosonic current and polarization induced by a magnetic flux running along a higher-dimensional cosmic string in the presence of a flat boundary orthogonal to the string. In our analysis, we assume that the quantum field obeys Dirichlet or Neunmann conditions on the flat boundary. To develop this analysis we calculate the corresponding positive frequency Wightman function. As consequence of the boundary condition, the Wightamn function is expressed in term of two contributions: The first one corresponds to the Wightman function in cosmic string spacetime in the absence of boundary, while the second one is induced by the presence of the boundary. Due to the fact that the analysis of induced bosonic current and polarization effects in the pure cosmic string spacetime have been developed by many authors, the main objective of this paper is to study the effects induced by the boundary. Regarding to the induced current, we show that, depending on the condition adopted, the boundary-induced azimuthal current can cancel or intensifies the total induced azimuthal current on the boundary; moreover, the boundary-induced azimuthal current is a periodic odd function of the magnetic flux. As to the vacuum expectation values of the field squared and the energy-momentum tensor, the boundary-induced contributions are even functions of magnetic flux. In particular, we consider some special cases of the boundary-induced part of the energy density and evaluate the normal vacuum force on the boundary.

Vacuum polarization by a flat boundary in cosmic string spacetime

In this paper, we analyze the vacuum expectation values of the field squared and the energy–momentum tensor associated with a massive scalar field in a higher dimensional cosmic string spacetime, obeying Dirichlet or Neumann boundary conditions on the surface orthogonal to the string. In order to develop this analysis, the corresponding Green's function is obtained. The Green's function is given by the sum of two expressions: the first one corresponds to the standard Green's function in the boundary-free cosmic string spacetime and the second contribution is induced by the boundary. The boundary-induced parts have opposite signs for Dirichlet and Neumann scalars. Because the analysis of vacuum polarization effects in the boundary-free cosmic string spacetime has been developed in the literature, here we are mainly interested in the calculations of the effects induced by the boundary. In this way closed expressions for the corresponding expectation values are provided, as well as their asymptotic behavior in different limiting regions being investigated. We show that the non-trivial topology due to the cosmic string enhances the boundary-induced vacuum polarization effects for both the field squared and the energy–momentum tensor, compared to the case of a boundary in Minkowski spacetime. The presence of the cosmic string induces non-zero stress along the direction normal to the boundary. The corresponding vacuum force acting on the boundary is investigated.

VACUUM POLARIZATION IN A COSMIC STRING SPACETIME INDUCED BY FLAT BOUNDARY

In this paper we analyze the vacuum expectation values of the field squared and the energy-momentum tensor associated to a massive scalar field in a higher dimensional cosmic string spacetime, obeying Dirichlet or Neumann boundary conditions on the surface orthogonal to the string.

Induced fermionic current densities by magnetic flux in higher dimensional cosmic string spacetime

In this paper, we analyze the vacuum fluctuations of quantum fermionic current densities, ⟨jA(x)⟩, induced by a magnetic flux running along the core of the conical space produced by the presence of cosmic string, in a (1 + d)-dimensional bulk, for 2 ⩽ d ⩽ 5. In order to develop this investigation, we construct an expression for the fermionic propagator, which can be applied for those different dimensions of the spacetime. Two specific analyses for the induced current densities are presented: (i) for massless fields in three and four dimensions and (ii) for massive fields in all dimensions considered. In the latter, specific values for the parameters which codify the presence of the cosmic string and the fractional part of the ratio of the magnetic flux to the quantum one are considered. Although being a very special situation and somewhat unnatural, the corresponding analysis of induced fermionic current densities under this circumstance may shed light on the qualitative behavior of these quantities in a more general situation.

Spinor Green function in higher-dimensional cosmic string space-time in the presence of magnetic flux

In this paper we investigate the vacuum polarization effects associated with quantum fermionic charged fields in a generalized $(d+1)-$dimensional cosmic string space-times considering the presence of a magnetic flux along the string. In order to develop this analysis we calculate a general expression for the respective Green function, valid for several different values of $d$, which is expressed in terms of a bispinor associated with the square of the Dirac operator. Adopting this result, we explicitly calculate the renormalized vacuum expectation values of the energy-momentum tensors, $ _{Ren.}$, associated with massless fields. Moreover, for specific values of the parameters which codify the cosmic string and the fractional part of the ratio of the magnetic flux by the quantum one, we were able to present in closed forms the bispinor and the respective Green function for massive fields.