84,173 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
Consistent picture for the electronic structure around a vortex core in iron-based superconductors
Based on a two-orbital model and taking into account the presence of the
impurity, we studied theoretically the electronic structure in the vortex core
of the iron-Pnictide superconducting materials. The vortex is pinned when the
impurity is close to the vortex core. The bound states shows up for the
unpinned vortex and are wiped out by a impurity. Our results are in good
agreement with recent experiments and present a consistent explanation for the
different electronic structure of vortex core revealed by experiments on
different materials.Comment: 4 pages, 5 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
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