706 research outputs found
Cosmological constant from quantum spacetime
http://dx.doi.org/10.1103/PhysRevD.91.124028© 2015, Physical Review
Heun equation, Teukolsky equation, and type-D metrics
Starting with the whole class of type-D vacuum backgrounds with cosmological
constant we show that the separated Teukolsky equation for zero rest-mass
fields with spin (gravitational waves), (electromagnetic
waves) and (neutrinos) is an Heun equation in disguise.Comment: 27 pages, corrected typo in eq. (1
Cylindrically symmetric, static strings with a cosmological constant in Brans-Dicke theory
The static, cylindrically symmetric vacuum solutions with a cosmological
constant in the framework of the Brans-Dicke theory are investigated. Some of
these solutions admitting Lorentz boost invariance along the symmetry axis
correspond to local, straight cosmic strings with a cosmological constant. Some
physical properties of such solutions are studied. These strings apply
attractive or repulsive forces on the test particles. A smooth matching is also
performed with a recently introduced interior thick string solution with a
cosmological constant.Comment: 8 pages, Revtex; Published versio
Cylindrical Solutions in Modified f(T) Gravity
We investigate static cylindrically symmetric vacuum solutions in Weyl
coordinates in the framework of f(T) theories of gravity, where T is the
torsion scalar. The set of modified Einstein equations is presented and the
fourth coming equations are established. Specific physical expressions are
assumed for the algebraic function f(T) and solutions are obtained. Moreover,
general solution is obtained with finite values of u(r) on the axis r = 0, and
this leads to a constant torsion scalar. Also, cosmological constant is
introduced and its relation to Linet-Tian solution in GR is commented.Comment: 13 pages; Accepted for publication in International Journal of Modern
Physics D (IJMPD
Asymptotically AdS Magnetic Branes in (n+1)-dimensional Dilaton Gravity
We present a new class of asymptotically AdS magnetic solutions in
()-dimensional dilaton gravity in the presence of an appropriate
combination of three Liouville-type potentials. This class of solutions is
asymptotically AdS in six and higher dimensions and yields a spacetime with
longitudinal magnetic field generated by a static brane. These solutions have
no curvature singularity and no horizons but have a conic geometry with a
deficit angle. We find that the brane tension depends on the dilaton field and
approaches a constant as the coupling constant of dilaton field goes to
infinity. We generalize this class of solutions to the case of spinning
magnetic solutions and find that, when one or more rotation parameters are
nonzero, the brane has a net electric charge which is proportional to the
magnitude of the rotation parameters. Finally, we use the counterterm method
inspired by AdS/CFT correspondence and compute the conserved quantities of
these spacetimes. We found that the conserved quantities do not depend on the
dilaton field, which is evident from the fact that the dilaton field vanishes
on the boundary at infinity.Comment: 15 page
Cylindrically Symmetric Vacuum Solutions in Higher Dimensional Brans-Dicke Theory
Higher dimensional, static, cylindrically symmetric vacuum solutions with and
without a cosmological constant in the Brans-Dicke theory are presented. We
show that, for a negative cosmological constant and for specific values of the
parameters, a particular subclass of these solutions include higher dimensional
topological black hole-type solutions with a flat horizon topology. We briefly
extend our discussion to stationary vacuum and vacuum solutions.Comment: V3: Published Versio
Multiple Photonic Shells Around a Line Singularity
Line singularities including cosmic strings may be screened by photonic
shells until they appear as a planar wall.Comment: 6 page
Disks in Expanding FRW Universes
We construct exact solutions to Einstein equations which represent
relativistic disks immersed into an expanding FRW Universe. It is shown that
the expansion influences dynamical characteristics of the disks such as
rotational curves, surface mass density, etc. The effects of the expansion is
exemplified with non-static generalizations of Kuzmin-Curzon and generalized
Schwarzschild disks.Comment: Revised version to appear in ApJ, Latex, 17 pages, 10 figures, uses
aaspp4 and epsf style file
The Levi-Civita spacetime
We consider two exact solutions of Einstein's field equations corresponding
to a cylinder of dust with net zero angular momentum. In one of the cases, the
dust distribution is homogeneous, whereas in the other, the angular velocity of
dust particles is constant [1]. For both solutions we studied the junction
conditions to the exterior static vacuum Levi-Civita spacetime. From this study
we find an upper limit for the energy density per unit length of the
source equal for the first case and for the second
one. Thus the homogeneous cluster provides another example [2] where the range
of is extended beyond the limit value previously found in
the literature [3,4]. Using the Cartan Scalars technics we show that the
Levi-Civita spacetime gets an extra symmetry for or
. We also find that the cluster of homogeneous dust has a superior
limit for its radius, depending on the constant volumetric energy density
Reparametrization-Invariant Path Integral in GR and "Big Bang" of Quantum Universe
The reparametrization-invariant generating functional for the unitary and
causal perturbation theory in general relativity in a finite space-time is
obtained. The region of validity of the Faddeev-Popov-DeWitt functional is
studied. It is shown that the invariant content of general relativity as a
constrained system can be covered by two "equivalent" unconstrained systems:
the "dynamic" (with "dynamic" evolution parameter as the metric scale factor)
and "geometric" (given by the Levi-Civita type canonical transformation to the
action-angle variables where the energy constraint converts into a new
momentum). "Big Bang", the Hubble evolution, and creation of matter fields by
the "geometric" vacuum are described by the inverted Levi-Civita (LC)
transformation of the geomeric system into the dynamic one. The particular case
of the LC transformations are the Bogoliubov ones of the particle variables
(diagonalizing the dynamic Hamiltonian) to the quasiparticles (diagonalizing
the equations of motion). The choice of initial conditions for the "Big Bang"
in the form of the Bogoliubov (squeezed) vacuum reproduces all stages of the
evolution of the Friedmann-Robertson-Walker Universe in their conformal
(Hoyle-Narlikar) versions.Comment: 21 pages, latex, 4 figures in postscrip
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