2,626 research outputs found
global monopole revisited
In this paper the global monopole is reexamined. We provide an exact
solution for the modified field equations in the presence of a global monopole
for regions outside its core, generalizing previous results. Additionally, we
discuss some particular cases obtained from this solution. We consider a setup
consisting of a possible Schwarzschild black hole that absorbs the topological
defect, giving rise to a static black hole endowed with a monopole's charge.
Besides, we demonstrate how the asymptotic behavior of the Higgs field far from
the monopole's core is shaped by a class of spacetime metrics which includes
those ones analyzed here. In order to assess the gravitational properties of
this system, we analyse the geodesic motion of both massive and massless test
particles moving in the vicinity of such configuration. For the material
particles we set the requirements they have to obey in order to experience
stable orbits. On the other hand, for the photons we investigate how their
trajectories are affected by the gravitational field of this black hole.Comment: 16 pages, 1 figure and 1 table. Minor changes to match published
version in EPJ
Vacuum Polarization for a Massless Spin-1/2 Field in the Global Monopole Spacetime at Nonzero Temperature
In this paper we present the effects produced by the temperature in the
renormalized vacuum expectation value of the zero-zero component of the
energy-momentum tensor associated with massless left-handed spinor field in the
pointlike global monopole spacetime. In order to develop this calculation we
had to obtain the Euclidean thermal Green function in this background. Because
the expression obtained for the thermal energy density cannot be expressed in a
closed form, its explicit dependence on the temperature is not completely
evident. So, in order to obtain concrete information about its thermal
behavior, we develop a numerical analysis of our result in the high-temperature
limit for specific values of the parameter which codify the presence
of the monopole.Comment: 22 pages, LaTex format, 5 figure
Remarks on some vacuum solutions of scalar-tensor cosmological models
We present a class of exact vacuum solutions corresponding to de Sitter and
warm inflation models in the framework of scalar-tensor cosmologies. We show
that in both cases the field equations reduce to planar dynamical systems with
constraints. Then, we carry out a qualitative analysis of the models by
examining the phase diagrams of the solutions near the equilibrium points.Comment: 12 pages, 4 figures. To be published in the Brazilian Journal of
Physic
Self-similar magnetoresistance of Fibonacci ultrathin magnetic films
We study numerically the magnetic properties (magnetization and
magnetoresistance) of ultra-thin magnetic films (Fe/Cr) grown following the
Fibonacci sequence. We use a phenomenological model which includes Zeeman,
cubic anisotropy, bilinear and biquadratic exchange energies. Our physical
parameters are based on experimental data recently reported, which contain
biquadratic exchange coupling with magnitude comparable to the bilinear
exchange coupling. When biquadratic exchange coupling is sufficiently large a
striking self-similar pattern emerges.Comment: 5 pages, 5 EPS figures, REVTeX, accepted for publication in Phys.
Rev.
Self-Forces on Electric and Magnetic Linear Sources in the Space-Time of a Cosmic String
In this paper we calculate the magnetic and electric self-forces, induced by
the conical structure of a cosmic string space-time, on a long straight wire
which presents either a constant current or a linear charge density. We also
show how these self-forces are related by a Lorentz tranformation and, in this
way, explain what two different inertial observers detect in their respective
frames.Comment: 10 pages, LaTeX, to be published in Phys. Rev. D
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