182 research outputs found
Non-singular black-holes on the brane
We investigate the possibility of obtaining non-singular black-hole solutions
in the brane world model by solving the effective field equations for the
induced metric on the brane. The Reissner-Nordstrom solution on the brane was
obtained by Dadhich etal by imposing the null energy condition on the 3-brane
for a bulk having non zero Weyl curvature. In this work, we relax the condition
of vanishing scalar curvature , however, retaining the null condition. We
have shown that it is possible to obtain class of static non-singular
spherically symmetric brane space-times admitting horizon. We obtain one such
class of solution which is a regular version of the Reissner-Nordstrom solution
in the standard general relativity.Comment: 8 pages, References added, Version to appear in Int. J. Mod. Phys.
A spacetime dual to the NUT spacetime
By decomposing the Riemann curvature into electric and magnetic parts, a
duality transformation, which involves interchange of active and passive
electric parts, has recently been proposed. It was shown that the Schwarzschild
solution is dual to the one that describes the Schwarzschild particle with
cloud of string dust or a global monopole. Following the same procedure we
obtain the solution dual to the NUT spacetime.Comment: 10 pages, Latex. Accepted for publication in Classical and Quantum
Gravit
The most general axially symmetric electrovac spacetime adimitting separable equations of motion
We obtain the most general solution of the Einstein electro - vacuum equation
for the stationary axially symmetric spacetime in which the Hamilton-Jacobi and
Klein - Gordon equations are separable. The most remarkable feature of the
solution is its invariance under the duality transformation involving mass and
NUT parameter, and the radial and angle coordinates. It is the general solution
for a rotating (gravitational dyon) particle which is endowed with both
gravoelectric and gravomagnetic charges, and there exists a duality
transformation from one to the other. It also happens to be a transform of the
Kerr - NUT solution. Like the Kerr family, it is also possible to make this
solution radiating which asymptotically conforms to the Vaidya null radiation.Comment: 9 pages, RevTex, Accepted by Class. Quantum Grav. Title, Abstract and
some expressions have been modified, typos corrected. The solution and main
result remain unaltere
A Conformal Mapping and Isothermal Perfect Fluid Model
Instead of conformal to flat spacetime, we take the metric conformal to a
spacetime which can be thought of as ``minimally'' curved in the sense that
free particles experience no gravitational force yet it has non-zero curvature.
The base spacetime can be written in the Kerr-Schild form in spherical polar
coordinates. The conformal metric then admits the unique three parameter family
of perfect fluid solution which is static and inhomogeneous. The density and
pressure fall off in the curvature radial coordinates as for
unbounded cosmological model with a barotropic equation of state. This is the
characteristic of isothermal fluid. We thus have an ansatz for isothermal
perfect fluid model. The solution can also represent bounded fluid spheres.Comment: 10 pages, TeX versio
To assess the prevalence and factors determining timely initiation of breastfeeding among the mothers in resettlement colony in Delhi
Background: The initiation of breastfeeding within 1 h of birth has various benefits and has been found to reduce neonatal mortality and morbidity. Objective: This study is designed to assess the prevalence and determinants of timely initiation of breastfeeding among mothers in a resettlement colony of Delhi. Materials and Methods: A community-based cross-sectional study was conducted in a resettlement colony of East Delhi among mothers with infants <6 months of age. Mothers were enrolled from Anganwadi Centers using systematic random sampling, and a questionnaire was used to record information on feeding practices. Chi-square test and multiple logistic regression analysis were performed. Results: The prevalence of the initiation of breastfeeding within 1 h of birth was 51.7%. Using multiple logistic regression analysis, the factors which were found to be significantly associated were type of delivery (p<0.005), place of delivery (p<0.005), and advice on the initiation of breastfeeding at the time of delivery or postnatal period (p<0.005). Conclusions: In this study, the prevalence of the initiation of breastfeeding is better than the national average. It was higher in children born in government health institutions. This study suggests that the importance of the early initiation of breastfeeding should be emphasized during antenatal care visits through trained skilled health professionals in public and private health sector
Entropy Bound and Causality Violation in Higher Curvature Gravity
In any quantum theory of gravity we do expect corrections to Einstein gravity
to occur. Yet, at fundamental level, it is not apparent what the most relevant
corrections are. We argue that the generic curvature square corrections present
in lower dimensional actions of various compactified string theories provide a
natural passage between the classical and quantum realms of gravity. The
Gauss-Bonnet and gravities, in particular, provide concrete
examples in which inconsistency of a theory, such as, a violation of
microcausality, and a classical limit on black hole entropy are correlated. In
such theories the ratio of the shear viscosity to the entropy density,
, can be smaller than for a boundary conformal field theory with
Einstein gravity dual. This result is interesting from the viewpoint that the
nuclear matter or quark-gluon plasma produced (such as at RHIC) under extreme
densities and temperatures may violate the conjectured bound , {\it albeit} marginally so.Comment: 23 pages, several eps figures; minor changes, references added,
published versio
Radiating black holes in Einstein-Yang-Mills theory and cosmic censorship
Exact nonstatic spherically symmetric black-hole solution of the higher
dimensional Einstein-Yang-Mills equations for a null dust with Yang-Mills gauge
charge are obtained by employing Wu-Yang \textit{ansatz}, namely, HD-EYM Vaidya
solution. It is interesting to note that gravitational contribution of YM gauge
charge for this ansatz is indeed opposite (attractive rather than repulsive)
that of Maxwell charge. It turns out that the gravitational collapse of null
dust with YM gauge charge admit strong curvature shell focusing naked
singularities violating cosmic censorship. However, there is significant
shrinkage of the initial data space for a naked singularity of the HD-Vaidya
collapse due to presence of YM gauge charge. The effect of YM gauge charge on
structure and location of the apparent and event horizons is also discussed.Comment: 9 RevTeX pages, 1 figur
Curvature driven acceleration : a utopia or a reality ?
The present work shows that a combination of nonlinear contribution from the
Ricci curvature in Einstein field equations can drive a late time acceleration
of expansion of the universe. The transit from the decelerated to the
accelerated phase of expansion takes place smoothly without having to resort to
a study of asymptotic behaviour. This result emphasizes the need for thorough
and critical examination of models with nonlinear contribution from the
curvature.Comment: 8 pages, 4 figure
On naked singularities in higher dimensional Vaidya space-times
We investigate the end state of gravitational collapse of null fluid in
higher dimensional space-times. Both naked singularities and black holes are
shown to be developing as final outcome of the collapse. The naked singularity
spectrum in collapsing Vaidya region (4D) gets covered with increase in
dimensions and hence higher dimensions favor black hole in comparison to naked
singularity. The Cosmic Censorship Conjecture will be fully respected for a
space of infinite dimension.Comment: 9 pages, LateX, Minor changes. Accepted in Phys. Rev.
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