5,691 research outputs found
Gravitational field equations in a braneworld with Euler-Poincare term
We present the effective gravitational field equations in a 3-brane world
with Euler-Poincare term and a cosmological constant in the bulk spacetime. The
similar equations on a 3-brane with symmetry embedded in a five
dimensional bulk spacetime were obtained earlier by Maeda and Torii using the
Gauss-Coddazzi projective approach in the framework of the Gaussian normal
coordinates. We recover these equations on the brane in terms of differential
forms and using a more general coordinate setting in the spirit of Arnowitt,
Deser and Misner (ADM). The latter allows for acceleration of the normals to
the brane surface through the lapse function and the shift vector. We show that
the gravitational effects of the bulk space are transmitted to the brane
through the projected ``electric'' 1-form field constructed from the conformal
Weyl curvature 2-form of the bulk space. We also derive the evolution equations
into the bulk space for the electric 1-form field, as well as for the
``magnetic'' 2-form field part of the bulk Weyl curvature 2-form. As expected,
unlike on-brane equations, the evolution equations involve terms determined by
the nonvanishing acceleration of the normals in the ADM-type slicing of
spacetime
Exact metric around a wiggly cosmic string
The exact metric around a wiggly cosmic string is found by modifying the
energy momentum-tensor of a straight infinitely thin cosmic string to include
an electric current along the symmetry axis.Comment: 5 page
Exact Solutions in Five-Dimensional Axi-dilaton Gravity with Euler-Poincare Term
We examine the effective field equations that are obtained from the
axi-dilaton gravity action with a second order Euler-Poincare term and a
cosmological constant in all higher dimensions. We solve these equations for
five-dimensional spacetimes possessing homogeneity and isotropy in their
three-dimensional subspaces. For a number of interesting special cases we show
that the solutions fall into two main classes: The first class consists of
time-dependent solutions with spherical or hyperboloidal symmetry which require
certain fine-tuning relations between the coupling constants of the model and
the cosmological constant. Solutions in the second class are locally static and
prove the validity of Birkhoff's staticity theorem in the axi-dilaton gravity.
We also give a special class of static solutions, among them the well-known
black hole solutions in which the usual electric charge is superseded by an
axion charge.Comment: New formulas and references adde
Vacuum Fluctuations of a massless spin-1/2 field around multiple cosmic strings
We study the interaction of a massless quantized spinor field with the
gravitational filed of N parallel static cosmic strings by using a perturbative
approach. We show that the presence of more than one cosmic string gives rise
to an additional contribution to the energy density of vacuum fluctuations,
thereby leading to a vacuum force attraction between two parallel cosmic
strings.Comment: Class. Quantum Grav. 14(1997) 321
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