509 research outputs found
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
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
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
Counterterm Method in Lovelock Theory and Horizonless Solutions in Dimensionally Continued Gravity
In this paper we, first, generalize the quasilocal definition of the stress
energy tensor of Einstein gravity to the case of Lovelock gravity, by
introducing the tensorial form of surface terms that make the action
well-defined. We also introduce the boundary counterterm that removes the
divergences of the action and the conserved quantities of the solutions of
Lovelock gravity with flat boundary at constant and . Second, we obtain
the metric of spacetimes generated by brane sources in dimensionally continued
gravity through the use of Hamiltonian formalism, and show that these solutions
have no curvature singularity and no horizons, but have conic singularity. We
show that these asymptotically AdS spacetimes which contain two fundamental
constants are complete. Finally we compute the conserved quantities of these
solutions through the use of the counterterm method introduced in the first
part of the paper.Comment: 15 pages, references added, typos correcte
Comparison between a new thyroglobulin assay with the well-established Beckman Access immunoassay: A preliminary report
Objectives: Measurement of serum thyroglobulin (Tg) plays a key role in the post-thyroidectomy management of differentiated thyroid carcinoma (DTC). In this context, the performance of new-generation thyroglobulin assay has clinical implications in the follow-up of DTC patients. Aim of this study was to compare the new highly sensitive Liaison Tg II (Tg-L) with the well-established Tg Access assay (Tg-A). Materials and methods: A total of 91 residual serum samples (23 positive and 68 negatives for Tg auto-antibodies) were tested by the Beckman Access and Diasorin Liaison assays. Study samples were from 21 patients with pathologically proven DTC and control samples from 70 (16 patients with benign thyroid disease and 54 apparently healthy subjects). Results: Our results showed that Tg-L was highly correlated with Tg-A for both values ranging between 0.2 and 50 ng/mL (Pearson's r = 0.933 [95%CI 0.894-0.958], P <.001) and higher than 50 ng/mL (Pearson's r = 0.849 [95%CI 0.609-0.946], P <.001). For Tg values lower than 0.2 ng/mL, the overall concordance rate was 92%. Moreover, we tested 7 fine-needle aspiration washout fluids (FNA), showing an overall concordance rate in discriminating negative and positive of 100%. Finally, we found no interference by Tg auto-antibodies (TgAbs) for both Tg-L and Tg-A. Conversely, rheumatoid factor (RF) interferes with Tg-A, but not with Tg-L in one patient with no relapsing thyroid carcinoma. Conclusions: Liaison Tg II demonstrated a good correlation with Access Tg assay both for sera and FNAs. Further studies on larger population are needed to evaluate Tg-L clinical impact on DTC patient's follow-up
Magnetic Strings in Dilaton Gravity
First, I present two new classes of magnetic rotating solutions in
four-dimensional Einstein-Maxwell-dilaton gravity with Liouville-type
potential. The first class of solutions yields a 4-dimensional spacetime with a
longitudinal magnetic field generated by a static or spinning magnetic string.
I find that these solutions have no curvature singularity and no horizons, but
have a conic geometry. In these spacetimes, when the rotation parameter does
not vanish, there exists an electric field, and therefore the spinning string
has a net electric charge which is proportional to the rotation parameter. The
second class of solutions yields a spacetime with an angular magnetic field.
These solutions have no curvature singularity, no horizon, and no conical
singularity. The net electric charge of the strings in these spacetimes is
proportional to their velocities. Second, I obtain the ()-dimensional
rotating solutions in Einstein-dilaton gravity with Liouville-type potential. I
argue that these solutions can present horizonless spacetimes with conic
singularity, if one chooses the parameters of the solutions suitable. I also
use the counterterm method and compute the conserved quantities of these
spacetimes.Comment: 16 pages, no figure, references added, some minor correction
Quantum healing of classical singularities in power-law spacetimes
We study a broad class of spacetimes whose metric coefficients reduce to
powers of a radius r in the limit of small r. Among these four-parameter
"power-law" metrics we identify those parameters for which the spacetimes have
classical singularities as r approaches 0. We show that a large set of such
classically singular spacetimes is nevertheless nonsingular quantum
mechanically, in that the Hamiltonian operator is essentially self-adjoint, so
that the evolution of quantum wave packets lacks the ambiguity associated with
scattering off singularities. Using these metrics, the broadest class yet
studied to compare classical with quantum singularities, we explore the
physical reasons why some that are singular classically are "healed" quantum
mechanically, while others are not. We show that most (but not all) of the
remaining quantum-mechanically singular spacetimes can be excluded if either
the weak energy condition or the dominant energy condition is invoked, and we
briefly discuss the effect of this work on the strong cosmic censorship
hypothesis.Comment: 14 pages, 1 figure; extensive revision
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