376 research outputs found
Concept for improved vacuum pressure measuring device
To measure vacuum pressures in the range of 5 times 10 to the minus 7 to 5 times 10 to the minus 16, a semiconductor resistor composed of sintered zinc oxide is used. Through the effect of surface absorbed gases on the resistance of the semiconductor material, very low pressures are measured
Far ultraviolet response of silicon P-N JUNCTION photodiodes
Silicon P-N junction photodiode resistivity in vacuum ultraviole
Anatomy of a Bounce
Holographic considerations are used in the scrutiny of a special class of
brane-world cosmologies. Inherently to this class, the brane typically bounces,
at a finite size, as a consequence of a charged black hole in the bulk. Whereas
a prior treatment [hep-th/0301010] emphasized a brane that is void of
standard-model matter, the analysis is now extended to include an intrinsic
(radiation-dominated) matter source. An interesting feature of this generalized
model is that a bounce is no longer guaranteed but, rather, depends on the
initial conditions. Ultimately, we demonstrate that compliance with an
appropriate holographic bound is a sufficient prerequisite for a bounce to
occur.Comment: 14 pages, Revtex; (v2) minor revisions; (v3) reference adde
Curvature tensors on distorted Killing horizons and their algebraic classification
We consider generic static spacetimes with Killing horizons and study
properties of curvature tensors in the horizon limit. It is determined that the
Weyl, Ricci, Riemann and Einstein tensors are algebraically special and
mutually aligned on the horizon. It is also pointed out that results obtained
in the tetrad adjusted to a static observer in general differ from those
obtained in a free-falling frame. This is connected to the fact that a static
observer becomes null on the horizon.
It is also shown that finiteness of the Kretschmann scalar on the horizon is
compatible with the divergence of the Weyl component or
in the freely falling frame. Furthermore finiteness of is compatible
with divergence of curvature invariants constructed from second derivatives of
the Riemann tensor.
We call the objects with finite Krestschmann scalar but infinite
``truly naked black holes''. In the (ultra)extremal versions of these objects
the structure of the Einstein tensor on the horizon changes due to extra terms
as compared to the usual horizons, the null energy condition being violated at
some portions of the horizon surface. The demand to rule out such divergencies
leads to the constancy of the factor that governs the leading term in the
asymptotics of the lapse function and in this sense represents a formal analog
of the zeroth law of mechanics of non-extremal black holes. In doing so, all
extra terms in the Einstein tensor automatically vanish.Comment: 21 pages, To appear in Class. Quant. Gra
Thermal Fluctuations and Black Hole Entropy
In this paper, we consider the effect of thermal fluctuations on the entropy
of both neutral and charged black holes. We emphasize the distinction between
fixed and fluctuating charge systems; using a canonical ensemble to describe
the former and a grand canonical ensemble to study the latter. Our novel
approach is based on the philosophy that the black hole quantum spectrum is an
essential component in any such calculation. For definiteness, we employ a
uniformly spaced area spectrum, which has been advocated by Bekenstein and
others in the literature. The generic results are applied to some specific
models; in particular, various limiting cases of an (arbitrary-dimensional)
AdS-Reissner-Nordstrom black hole. We find that the leading-order quantum
correction to the entropy can consistently be expressed as the logarithm of the
classical quantity. For a small AdS curvature parameter and zero net charge, it
is shown that, independent of the dimension, the logarithmic prefactor is +1/2
when the charge is fixed but +1 when the charge is fluctuating.We also
demonstrate that, in the grand canonical framework, the fluctuations in the
charge are large, , even when .
A further implication of this framework is that an asymptotically flat,
non-extremal black hole can never achieve a state of thermal equilibrium.Comment: 25 pages, Revtex; references added and corrected, and some minor
change
Of Bounces, Branes and Bounds
Some recent studies have considered a Randall-Sundrum-like brane world
evolving in the background of an anti-de Sitter Reissner-Nordstrom black hole.
For this scenario, it has been shown that, when the bulk charge is
non-vanishing, a singularity-free ``bounce'' universe will always be obtained.
However, for the physically relevant case of a de Sitter brane world, we have
recently argued that, from a holographic (c-theorem) perspective, such brane
worlds may not be physically viable. In the current paper, we reconsider the
validity of such models by appealing to the so-called ``causal entropy bound''.
In this framework, a paradoxical outcome is obtained: these brane worlds are
indeed holographically viable, provided that the bulk charge is not too small.
We go on to argue that this new finding is likely the more reliable one.Comment: 15 pages, Revtex; references added and very minor change
A Commentary on Ruppeiner Metrics for Black Holes
There has been some recent controversy regarding the Ruppeiner metrics that
are induced by Reissner-Nordstrom (and Reissner-Nordstrom-like) black holes.
Most infamously, why does this family of metrics turn out to be flat, how is
this outcome to be physically understood, and can/should the formalism be
suitably modified to induce curvature? In the current paper, we provide a novel
interpretation of this debate. For the sake of maximal analytic clarity and
tractability, some supporting calculations are carried out for the relatively
simple model of a rotating BTZ black hole.Comment: 15 pages; v2, typos corrected and a few references adde
Problems with Tunneling of Thin Shells from Black Holes
It is shown that is not invariant under canonical
transformations in general. Specifically for shells tunneling out of black
holes, this quantity is not invariant under canonical transformations. It can
be interpreted as the transmission coefficient only in the cases in which it is
invariant under canonical transformations. Although such cases include alpha
decay, they do not include the tunneling of shells from black holes. The
simplest extension to this formula which is invariant under canonical
transformations is proposed. However it is shown that this gives half the
correct temperature for black holes.Comment: 25 pages, 3 figures; v4: Made changes for publicatio
The Highly Damped Quasinormal Modes of -dimensional Reissner-Nordstrom Black Holes in the Small Charge Limit
We analyze in detail the highly damped quasinormal modes of -dimensional
Reissner-Nordstrm black holes with small charge, paying
particular attention to the large but finite damping limit in which the
Schwarzschild results should be valid. In the infinite damping limit, we
confirm using different methods the results obtained previously in the
literature for higher dimensional Reissner-Nordstrm black holes.
Using a combination of analytic and numerical techniques we also calculate the
transition of the real part of the quasinormal mode frequency from the
Reissner-Nordstrm value for very large damping to the
Schwarzschild value of for intermediate damping. The real
frequency does not interpolate smoothly between the two values. Instead there
is a critical value of the damping at which the topology of the
Stokes/anti-Stokes lines change, and the real part of the quasinormal mode
frequency dips to zero.Comment: 18 pages, 8 figure
Spectrum of Charged Black Holes - The Big Fix Mechanism Revisited
Following an earlier suggestion of the authors(gr-qc/9607030), we use some
basic properties of Euclidean black hole thermodynamics and the quantum
mechanics of systems with periodic phase space coordinate to derive the
discrete two-parameter area spectrum of generic charged spherically symmetric
black holes in any dimension. For the Reissner-Nordstrom black hole we get
, where the integer p=0,1,2,.. gives the charge
spectrum, with . The quantity , n=0,1,... gives
a measure of the excess of the mass/energy over the critical minimum (i.e.
extremal) value allowed for a given fixed charge Q. The classical critical
bound cannot be saturated due to vacuum fluctuations of the horizon, so that
generically extremal black holes do not appear in the physical spectrum.
Consistency also requires the black hole charge to be an integer multiple of
any fundamental elementary particle charge: , m=0,1,2,.... As a
by-product this yields a relation between the fine structure constant and
integer parameters of the black hole -- a kind of the Coleman big fix mechanism
induced by black holes. In four dimensions, this relationship is
and requires the fine structure constant to be a rational
number. Finally, we prove that the horizon area is an adiabatic invariant, as
has been conjectured previously.Comment: 21 pages, Latex. 1 Section, 1 Figure added. To appear in Class. and
Quant. Gravit
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