747 research outputs found
Large Area Crop Inventory Experiment (LACIE). Intensive test site assessment report
There are no author-identified significant results in this report
Exact soluble two-dimensional charged wormhole
We present an exactly soluble charged wormhole model in two dimensions by
adding infalling chiral fermions on the static wormhole. The infalling energy
due to the infalling charged matter requires the classical back reaction of the
geometry, which is solved by taking into account of the nontrivial nonchiral
exotic energy. Finally, we obtain the exact expression for the size of the
throat depending on the total amount of the infalling net energy and discuss
the interesting transition from the AdS spacetime to the wormhole geometry.Comment: 8 pages, no figure
Black Hole Thermodynamics and Two-Dimensional Dilaton Gravity Theory
We relate various black hole solutions in the near-horizon region to black
hole solutions in two-dimensional dilaton gravity theories in order to argue
that thermodynamics of black holes in D>=4 can be effectively described by
thermodynamics of black holes in two-dimensional dilaton gravity theories. We
show that the Bekenstein-Hawking entropies of single-charged dilatonic black
holes and dilatonic p-branes with an arbitrary dilaton coupling parameter in
arbitrary spacetime dimensions are exactly reproduced by the Bekenstein-Hawking
entropy of the two-dimensional black hole in the associated two-dimensional
dilaton gravity model. We comment that thermodynamics of non-extreme stringy
four-dimensional black hole with four charges and five-dimensional black hole
with three charges may be effectively described by thermodynamics of the black
hole solutions with constant dilaton field in two-dimensional dilaton gravity
theories.Comment: 15 pages, LaTeX, added reference
Flat World of Dilatonic Domain Walls
We study dilatonic domain walls specific to superstring theory.
Along with the matter fields and metric the dilaton also changes its value in
the wall background. We found supersymmetric (extreme) solutions which in
general interpolate between isolated superstring vacua with non-equal value of
the matter potential; they correspond to the static, planar domain walls with
{\it flat} metric in the string (sigma model) frame.
We point out similarities between the space-time of dilatonic walls and that
of charged dilatonic black holes. We also comment on non-extreme solutions
corresponding to expanding bubbles.Comment: 11 pgs (+2 figures available upon request), UPR-560-
Radiative Kaon Decays and Direct CP Violation
It is stressed that a measurement of the electric dipole amplitude for direct
photon emission in \kpm decays through its interference with inner
bremsstrahlung is important for differentiating among various models. Effects
of amplitude CP violation in the radiative decays of the charged kaon are
analyzed in the Standard Model in conjunction with the large approach. We
point out that gluon and electromagnetic penguin contributions to the
CP-violating asymmetry between the Dalitz plots of \kpm are of equal weight.
The magnitude of CP asymmetry ranges from to when the photon energy in the kaon rest frame varies from 50 MeV to
170 MeV.Comment: Latex, 11 pages, ITP-SB-93-36, IP-ASTP-22-9
Finite Black Hole Entropy and String Theory
An accelerating observer sees a thermal bath of radiation at the Hawking
temperature which is proportional to the acceleration. Also, in string theory
there is a Hagedorn temperature beyond which one cannot go without an infinite
amount of energy. Several authors have shown that in the context of Hawking
radiation a limiting temperature for string theory leads to a limiting
acceleration, which for a black hole implies a minimum distance from the
horizon for an observer to remain stationary. We argue that this effectively
introduces a cutoff in Rindler space or the Schwarzschild geometry inside of
which accelerations would exceed this maximum value. Furthermore, this natural
cutoff in turn allows one to define a finite entropy for Rindler space or a
black hole as all divergences were occurring on the horizon. In all cases if a
particular relationship exists between Newton's constant and the string tension
then the entropy of the string modes agrees with the Bekenstein-Hawking
formula.Comment: 17 pages, 1 figure, Florida Preprint UFIFT-HEP-94-0
DNA Nucleobase Synthesis at Titan Atmosphere Analog by Soft X-rays
Titan, the largest satellite of Saturn, has an atmosphere chiefly made up of
N2 and CH4 and includes traces of many simple organic compounds. This
atmosphere also partly consists of haze and aerosol particles which during the
last 4.5 gigayears have been processed by electric discharges, ions, and
ionizing photons, being slowly deposited over the Titan surface. In this work,
we investigate the possible effects produced by soft X-rays (and secondary
electrons) on Titan aerosol analogs in an attempt to simulate some prebiotic
photochemistry. The experiments have been performed inside a high vacuum
chamber coupled to the soft X-ray spectroscopy beamline at the Brazilian
Synchrotron Light Source, Campinas, Brazil. In-situ sample analyses were
performed by a Fourier transform infrared spectrometer. The infrared spectra
have presented several organic molecules, including nitriles and aromatic CN
compounds. After the irradiation, the brownish-orange organic residue (tholin)
was analyzed ex-situ by gas chromatographic (GC/MS) and nuclear magnetic
resonance (1H NMR) techniques, revealing the presence of adenine (C5H5N5), one
of the constituents of the DNA molecule. This confirms previous results which
showed that the organic chemistry on the Titan surface can be very complex and
extremely rich in prebiotic compounds. Molecules like these on the early Earth
have found a place to allow life (as we know) to flourish.Comment: To appear in Journal of Physical Chemistry A.; Number of pages: 6;
Number of Figures: 5; Number of Tables: 1; Number of references:49; Full
paper at http://pubs.acs.org/doi/abs/10.1021/jp902824
Quantum (in)stability of 2D charged dilaton black holes and 3D rotating black holes
The quantum properties of charged black holes (BHs) in 2D dilaton-Maxwell
gravity (spontaneously compactified from heterotic string) with dilaton
coupled scalars are studied. We first investigate 2D BHs found by McGuigan,
Nappi and Yost. Kaluza-Klein reduction of 3D gravity with minimal scalars leads
also to 2D dilaton-Maxwell gravity with dilaton coupled scalars and the
rotating BH solution found by Ba\~nados, Teitelboim and Zanelli (BTZ) which can
be also described by 2D charged dilatonic BH. Evaluating the one-loop effective
action for dilaton coupled scalars in large (and s-wave approximation for
BTZ case), we show that quantum-corrected BHs may evaporate or else
anti-evaporate similarly to 4D Nariai BH as is observed by Bousso and Hawking.
Higher modes may cause the disintegration of BH in accordance with recent
observation by Bousso.Comment: LaTeX file and ps files for figures, new section is added, title is
change
Black Hole Entropy without Brick Walls
We present evidence which confirms a suggestion by Susskind and Uglum
regarding black hole entropy. Using a Pauli-Villars regulator, we find that 't
Hooft's approach to evaluating black hole entropy through a
statistical-mechanical counting of states for a scalar field propagating
outside the event horizon yields precisely the one-loop renormalization of the
standard Bekenstein-Hawking formula, S=\A/(4G). Our calculation also yields a
constant contribution to the black hole entropy, a contribution associated with
the one-loop renormalization of higher curvature terms in the gravitational
action.Comment: 15 pages, plain LaTex minor additions including some references;
version accepted for publicatio
Dimensional reduction of 4d heterotic string black holes
We perform the spherical symmetric dimensional reduction of
heterotic string theory. We find a class of two-dimensional (2d) dilaton
gravity models that gives a general description of the near-horizon,
near-extremal behavior of four-dimensional (4d) heterotic string black holes.
We show that the duality group of the 4d theory is realized in two dimensions
in terms of Weyl transformations of the metric. We use the 2d dilaton gravity
theory to compute the statistical entropy of the near-extremal 4d,
, black hole.Comment: 12 pages, LaTex fil
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