62,087 research outputs found
Collapsing and static thin massive charged dust shells in a Reissner-Nordstr\"om black hole background in higher dimensions
The problem of a spherically symmetric charged thin shell of dust collapsing
gravitationally into a charged Reissner-Nordstr\"om black hole in spacetime
dimensions is studied within the theory of general relativity. Static charged
shells in such a background are also analyzed. First a derivation of the
equation of motion of such a shell in a -dimensional spacetime is given.
Then a proof of the cosmic censorship conjecture in a charged collapsing
framework is presented, and a useful constraint which leads to an upper bound
for the rest mass of a charged shell with an empty interior is derived. It is
also proved that a shell with total mass equal to charge, i.e., an extremal
shell, in an empty interior, can only stay in neutral equilibrium outside its
gravitational radius. This implies that it is not possible to generate a
regular extremal black hole by placing an extremal dust thin shell within its
own gravitational radius. Moreover, it is shown, for an empty interior, that
the rest mass of the shell is limited from above. Then several types of
behavior of oscillatory charged shells are studied. In the presence of a
horizon, it is shown that an oscillatory shell always enters the horizon and
reemerges in a new asymptotically flat region of the extended
Reissner-Nordstr\"om spacetime. On the other hand, for an overcharged interior,
i.e., a shell with no horizons, an example showing that the shell can achieve a
stable equilibrium position is presented. The results presented have
applications in brane scenarios with extra large dimensions, where the creation
of tiny higher dimensional charged black holes in current particle accelerators
might be a real possibility, and generalize to higher dimensions previous
calculations on the dynamics of charged shells in four dimensions.Comment: 21 pages, 2 figure
The Tolman-Bondi--Vaidya Spacetime: matching timelike dust to null dust
The Tolman-Bondi and Vaidya solutions are two solutions to Einstein equations
which describe dust particles and null fluid, respectively. We show that it is
possible to match the two solutions in one single spacetime, the
Tolman-Bondi--Vaidya spacetime. The new spacetime is divided by a null surface
with Tolman-Bondi dust on one side and Vaidya fluid on the other side. The
differentiability of the spacetime is discussed. By constructing a specific
solution, we show that the metric across the null surface can be at least
and the stress-energy tensor is continuous.Comment: 5 pages, no figur
Cryptanalysis of the Hillery-Buzek-Berthiaume quantum secret-sharing protocol
The participant attack is the most serious threat for quantum secret-sharing
protocols. We present a method to analyze the security of quantum
secret-sharing protocols against this kind of attack taking the scheme of
Hillery, Buzek, and Berthiaume (HBB) [Phys. Rev. A 59 1829 (1999)] as an
example. By distinguishing between two mixed states, we derive the necessary
and sufficient conditions under which a dishonest participant can attain all
the information without introducing any error, which shows that the HBB
protocol is insecure against dishonest participants. It is easy to verify that
the attack scheme of Karlsson, Koashi, and Imoto [Phys. Rev. A 59, 162 (1999)]
is a special example of our results. To demonstrate our results further, we
construct an explicit attack scheme according to the necessary and sufficient
conditions. Our work completes the security analysis of the HBB protocol, and
the method presented may be useful for the analysis of other similar protocols.Comment: Revtex, 7 pages, 3 figures; Introduction modifie
Entropy in the NUT-Kerr-Newman Black Holes Due to an Arbitrary Spin Field
Membrane method is used to compute the entropy of the NUT-Kerr-Newman black
holes. It is found that even though the Euler characteristic is greater than
two, the Bekenstein-Hawking area law is still satisfied. The formula relating the entropy and the Euler characteristic becomes inapplicable for
non-extreme four dimensional NUT-Kerr-Newman black holes
Search for Spin-Dependent Short-Range Force Using Optically Polarized He Gas
We propose a new method to detect short-range \textit{P-} and \textit{T-}
violating interactions between nucleons, based on measuring the precession
frequency shift of polarized He nuclei in the presence of an unpolarized
mass. To maximize the sensitivity, a high-pressure He cell with thin glass
windows (250 ) is used to minimize the distance between the mass and
He. The magnetic field fluctuation is suppressed by using the He gas in
a different region of the cell as a magnetometer. Systematic uncertainties from
the magnetic properties of the mass are suppressed by flipping both the
magnetic field and spin directions. Without any magnetic shielding, our result
has already reached the sensitivity of the current best limit. With improvement
in uniformity and stability of the field, we can further improve the
sensitivity by two orders of magnitude over the force range from
m
meson broadening and dilepton production in heavy ion collisions
The modification of the width of the rho meson due to in-medium decays and
collisions is evaluated. In high temperature and/or high density hadronic
matter, the collision width is much larger than the one-loop decay width. The
large width of the meson in matter seems to be consistent with some
current interpretations of the mass spectra measured at the CERN/SPS.Comment: 4 pages, LaTeX, including 4 Postscript figures, to appear in Proc. of
QM'99, Nucl. Phys.
Benchmark of FEM, Waveguide and FDTD Algorithms for Rigorous Mask Simulation
An extremely fast time-harmonic finite element solver developed for the
transmission analysis of photonic crystals was applied to mask simulation
problems. The applicability was proven by examining a set of typical problems
and by a benchmarking against two established methods (FDTD and a differential
method) and an analytical example. The new finite element approach was up to
100 times faster than the competing approaches for moderate target accuracies,
and it was the only method which allowed to reach high target accuracies.Comment: 12 pages, 8 figures (see original publication for images with a
better resolution
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