2,968 research outputs found
Generalization of the model of Hawking radiation with modified high frequency dispersion relation
The Hawking radiation is one of the most interesting phenomena predicted by
the theory of quantum field in curved space. The origin of Hawking radiation is
closely related to the fact that a particle which marginally escapes from
collapsing into a black hole is observed at the future infinity with infinitely
large redshift. In other words, such a particle had a very high frequency when
it was near the event horizon. Motivated by the possibility that the property
of Hawking radiation may be altered by some unknowned physics which may exist
beyond some critical scale, Unruh proposed a model which has higher order
spatial derivative terms. In his model, the effects of unknown physics are
modeled so as to be suppressed for the waves with a wavelength much longer than
the critical scale, . Surprisingly, it was shown that the thermal
spectrum is recovered for such modified models. To introduce such higher order
spatial derivative terms, the Lorentz invariance must be violated because one
special spatial direction needs to be chosen. In previous works, the rest frame
of freely-falling observers was employed as this special reference frame. Here
we give an extension by allowing a more general choice of the reference frame.
Developing the method taken by Corley, % and especially focusing on subluminal
case, we show that the resulting spectrum of created particles again becomes
the thermal one at the Hawking temperature even if the choice of the reference
frame is generalized. Using the technique of the matched asymptotic expansion,
we also show that the correction to the thermal radiation stays of order
or smaller when the spectrum of radiated particle around its peak is
concerned.Comment: 23 pages, 5 postscript figures, submitted to Physical Review
Origin of the Thermal Radiation in a Solid-State Analog of a Black-Hole
An effective black-hole-like horizon occurs, for electromagnetic waves in
matter, at a surface of singular electric and magnetic permeabilities. In a
physical dispersive medium this horizon disappears for wave numbers with
. Nevertheless, it is shown that Hawking radiation is still emitted if
free field modes with are in their ground state.Comment: 13 Pages, 3 figures, Revtex with epsf macro
The Holographic Principle for General Backgrounds
We aim to establish the holographic principle as a universal law, rather than
a property only of static systems and special space-times. Our covariant
formalism yields an upper bound on entropy which applies to both open and
closed surfaces, independently of shape or location. It reduces to the
Bekenstein bound whenever the latter is expected to hold, but complements it
with novel bounds when gravity dominates. In particular, it remains valid in
closed FRW cosmologies and in the interior of black holes. We give an explicit
construction for obtaining holographic screens in arbitrary space-times (which
need not have a boundary). This may aid the search for non-perturbative
definitions of quantum gravity in space-times other than AdS.Comment: 15 pages, 4 figures. Based on a talk given at Strings '99. Includes a
reply to recent criticism. For more details, examples, and references, see
hep-th/9905177 and hep-th/990602
Bubbling 1/2 BPS Geometries and Penrose Limits
We discuss how to take a Penrose limit in bubbling 1/2 BPS geometries at the
stage of a single function z(x_1,x_2,y). By starting from the z of the AdS_5 x
S^5 we can directly derive that of the pp-wave via the Penrose limit. In that
time the function z for the pp-wave with 1/R^2-corrections is obtained. We see
that it surely reproduces the pp-wave with 1/R^2 terms. In addition we consider
the Penrose limit in the configuration of the concentric rings.Comment: 15 pages, 3 figures, LaTeX, v2:higher order corrections are added,
typos corrected and references added, version to appear in PR
Lattice Black Holes
We study the Hawking process on lattices falling into static black holes. The
motivation is to understand how the outgoing modes and Hawking radiation can
arise in a setting with a strict short distance cutoff in the free-fall frame.
We employ two-dimensional free scalar field theory. For a falling lattice with
a discrete time-translation symmetry we use analytical methods to establish
that, for Killing frequency and surface gravity satisfying
in lattice units, the continuum Hawking spectrum
is recovered. The low frequency outgoing modes arise from exotic ingoing modes
with large proper wavevectors that "refract" off the horizon. In this model
with time translation symmetry the proper lattice spacing goes to zero at
spatial infinity. We also consider instead falling lattices whose proper
lattice spacing is constant at infinity and therefore grows with time at any
finite radius. This violation of time translation symmetry is visible only at
wavelengths comparable to the lattice spacing, and it is responsible for
transmuting ingoing high Killing frequency modes into low frequency outgoing
modes.Comment: 26 pages, LaTeX, 2 figures included with psfig. Several improvements
in the presentation. One figure added. Final version to appear in Phys.Rev.
Asking the Right Questions: Accessibility and Library Study Rooms
This article assists administrators who want to ensure their libraries are inclusive of people with disabilities but donât know where to start. We argue that organizations should understand not only the basic dimensions of ADA law but also dimensions of disability. They should also become familiar with multiple domains of disability and proactively incorporate reflective questions posed by researchers and advocates into the library space planning process. The article uses examples of common missteps in the development of study rooms with some reflection on how to learn from the experience
Collapse of Kaluza-Klein Bubbles
Kaluza-Klein theory admits ``bubble" configurations, in which the
circumference of the fifth dimension shrinks to zero on some compact surface. A
three parameter family of such bubble initial data at a moment of time-symmetry
(some including a magnetic field) has been found by Brill and Horowitz,
generalizing the (zero-energy) ``Witten bubble" solution. Some of these data
have negative total energy. We show here that all the negative energy bubble
solutions start out expanding away from the moment of time symmetry, while the
positive energy bubbles can start out either expanding or contracting. Thus it
is unlikely that the negative energy bubbles would collapse and produce a naked
singularity.Comment: 6 pages, plain LaTeX, UMDGR-94-08
Wheat Transportation in Perspective
This publication discusses the history of the various types of transportation used to get wheat to market. The historic importance of railways in wheat transportation and railroad regulation, as well as the role of trucks and barges, is also explained
Gravity on Noncommutative D-Branes
The effective action for the low energy scattering of two gravitons with a
D-brane in the presence of a constant antisytmetric field in bosonic string
theory is calculated and the modification to the standard D-brane action to
first order in is obtained.Comment: 18 pages, Latex file, accepted in Int. J. Mod. Phys.
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