37,406 research outputs found
A nonsingular rotating black hole
The spacetime singularities in classical general relativity are inevitable,
which are also predicated by the celebrated singularity theorems. However, it
is general belief that singularities do not exist in the nature and they are
the limitations of the general relativity. In the absence of a well defined
quantum gravity, models of regular black holes have been studied. We employ
probability distribution inspired mass function to replace Kerr black
hole mass to present a nonsingular rotating black hole that is identified
asymptotically (, constant) exactly as the Kerr-Newman black
hole, and as the Kerr black hole when . The radiating counterpart renders
a nonsingular generalization of Carmeli's spacetime as well as Vaidya's
spacetime, in the appropriate limits. The exponential correction factor
changing the geometry of the classic black hole to remove curvature singularity
can be also motivated by the quantum arguments. The regular rotating spacetime
can also be understood as a black hole of general relativity coupled to
nonlinear electrodynamics.Comment: 13 pages, 5 figures, 1 table, several changes, accepted in EPJC (as
Letter
Rotating black hole and quintessence
We discuss spherically symmetric exact solutions of the Einstein equations
for quintessential matter surrounding a black hole, which has an additional
parameter () due to the quintessential matter, apart from the mass
(). In turn, we employ the NewmanJanis complex transformation to this
spherical quintessence black hole solution and present a rotating counterpart
that is identified, for and , exactly as the
KerrNewman black hole, and as the Kerr black hole when .
Interestingly, for a given value of parameter , there exists a critical
rotation parameter (), which corresponds to an extremal black hole
with degenerate horizons, while for , it describes a non-extremal
black hole with Cauchy and event horizons, and no black hole for . We
find that the extremal value is also influenced by the parameter
and so is the ergoregion.Comment: 14 pages, 3 figures, 3 tables, accepted for publication EPJC (Letter
Small Area Shrinkage Estimation
The need for small area estimates is increasingly felt in both the public and
private sectors in order to formulate their strategic plans. It is now widely
recognized that direct small area survey estimates are highly unreliable owing
to large standard errors and coefficients of variation. The reason behind this
is that a survey is usually designed to achieve a specified level of accuracy
at a higher level of geography than that of small areas. Lack of additional
resources makes it almost imperative to use the same data to produce small area
estimates. For example, if a survey is designed to estimate per capita income
for a state, the same survey data need to be used to produce similar estimates
for counties, subcounties and census divisions within that state. Thus, by
necessity, small area estimation needs explicit, or at least implicit, use of
models to link these areas. Improved small area estimates are found by
"borrowing strength" from similar neighboring areas.Comment: Published in at http://dx.doi.org/10.1214/11-STS374 the Statistical
Science (http://www.imstat.org/sts/) by the Institute of Mathematical
Statistics (http://www.imstat.org
Modelling Two-Roton Bound State Formation in Fractional Quantum Hall System
Composite Fermion approach using extensive and parallalized numerical
analysis has recently established a two-roton bound state as the lowest energy
long wavelength neutral excitation of FQHE for finite particle (N~30) system.
By focussing on the "oriented dipole" character of magneto roton, we model the
two roton problem and solve it variationally (analytically) to find a two-roton
bound state with binding energy which is in good agreement with the composite
fermion numerical results.Comment: 4 pages, REVTEX file, 3 figures, Minor changes, Accepted for
publication in Physical Review Letter
Rotating black hole in Rastall theory
Rotating black hole solutions in theories of modified gravity are important
as they offer an arena to test these theories through astrophysical
observation. The non-rotating black hole can be hardly tested since the black
hole spin is very important in any astrophysical process. We present rotating
counterpart of a recently obtained spherically symmetric exact black hole
solution surrounded by perfect fluid in the context of Rastall theory, viz,
rotating Rastall black hole that generalize the Kerr-Newman black hole
solution. In turn, we analyze the specific cases of the Kerr-Newman black holes
surrounded by matter like dust and quintessence fields. Interestingly, for a
set of parameters and a chosen surrounding field, there exists a critical
rotation parameter (), which corresponds to an extremal black hole
with degenerate horizons, while for , it describes a non-extremal
black hole with Cauchy and event horizons, and no black hole for with
value is also influenced by these parameters. We also discuss the
thermodynamical quantities associated with rotating Rastall black hole, and
analyze the particle motion with the behavior of effective potential.Comment: 26 pages, 8 figures. Matched with the published versio
Rotating Hayward's regular black hole as particle accelerator
Recently, Ban\~{a}dos, Silk and West (BSW) demonstrated that the extremal
Kerr black hole can act as a particle accelerator with arbitrarily high
center-of-mass energy () when the collision takes place near the
horizon. The rotating Hayward's regular black hole, apart from Mass () and
angular momentum (), has a new parameter ( is a constant) that
provides a deviation from the Kerr black hole. We demonstrate that for each
, with , there exist critical and , which
corresponds to a regular extremal black hole with degenerate horizon, and
decreases and increases with increase in . While
describe a regular non-extremal black hole with outer and inner
horizons. We apply BSW process to the rotating Hayward's regular black hole,
for different , and demonstrate numerically that diverges in the
vicinity of the horizon for the extremal cases, thereby suggesting that a
rotating regular black hole can also act as a particle accelerator and thus in
turn may provide a suitable framework for Plank-scale physics. For a
non-extremal case, there always exist a finite upper bound of , which
increases with deviation parameter .Comment: 10 pages, 10 figures, 4 tables, accepted to be published in Journal
of High Energy Physic
Spinning Higher Dimensional Einstein-Yang-Mills black holes
We construct a Kerr-Newman-like spacetimes starting from higher dimensional
(HD) Einstein-Yang-Mills black holes via complex transformations suggested by
Newman-Janis. The new metrics are HD generalization of Kerr-Newman spacetimes
which has a geometry precisely that of Kerr-Newman in 4D corresponding to
Yang-Mills (YM) gauge charge, but the sign of charge term gets flipped in the
HD spacetimes. It is interesting to note that gravitational contribution of YM
gauge charge, in HD, is indeed opposite (attractive rather than repulsive) that
of Maxwell charge. The effect of YM gauge charge on the structure and location
of static limit surface and apparent horizon is discussed. We find that static
limit surfaces become less prolate with increase in dimensions and are also
sensitive to YM gauge charge thereby affecting the shape of ergosphere. We also
analyze some thermodynamical properties of these BHs.Comment: Accepted for publication in EPJ
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