1,325 research outputs found
Vacuum polarization by topological defects in de Sitter spacetime
In this paper we investigate the vacuum polarization effects associated with
a massive quantum scalar field in de Sitter spacetime in the presence of
gravitational topological defects. Specifically we calculate the vacuum
expectation value of the field square, . Because this investigation
has been developed in a pure de Sitter space, here we are mainly interested on
the effects induced by the presence of the defects.Comment: Talk presented at the 1st. Mediterranean Conference on Classical and
Quantum Gravity (MCCQG
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
Ground State Energy of Massive Scalar Field Inside a Spherical Region in the Global Monopole Background
Using the zeta function regularization method we calculate the ground state
energy of scalar massive field inside a spherical region in the space-time of a
point-like global monopole. Two cases are investigated: (i) We calculate the
Casimir energy inside a sphere of radius and make an analytical analysis
about it. We observe that this energy may be positive or negative depending on
metric coefficient and non-conformal coupling . In the limit
we found a zero result. (ii) In the second model we surround the
monopole by additional sphere of radius and consider scalar field
confined in the region between these two spheres. In the latter, the ground
state energy presents an additional contribution due to boundary at which
is divergent for small radius. Additional comments about renormalization are
considered.Comment: 30 pages and 2 figures. LATEX fil
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, ,
admitting a non-minimal coupling between the field with the geometry: $\xi
{\cal{R}}\hat{\Phi}^2$. Also we calculate the corrections on the vacuum
expectation value of the energy-momentum tensor, , 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 , the corrections caused by the inner structure of the
monopole can provide relevant contributions on these vacuum polarizations.Comment: Accepted for publication in Classical and Quantum Gravity. Added
references. 22 pages, 1 figur
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.Comment: 21 pages, 5 figure
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 in the Spacetime of Multiple Cosmic Strings
We calculate the electromagnetic self-force on a stationary linear
distribution of four-current in the spacetime of multiple cosmic strings. It is
shown that if the current is infinitely thin and stretched along a line which
is parallel to the strings the problem admits an explicit solution.Comment: This paper has been produced in Latex format and has 18 page
Vacuum Polarization of Massless Spinor Field in Global Monopole Spacetime
We calculate the renormalized vacuum average of the energy-momentum tensor of
massless left-handed spinor field in the pointlike global monopole spacetime
using point-separation approach. The general structure of the vacuum average of
the energy-momentum tensor is obtained and expressed in terms of
component, explicit form of which is analyzed in great details
for arbitrary solid angle deficit.Comment: 12 pages, REVTEX, print error was correcte
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