2,145 research outputs found
Static and symmetric wormholes respecting energy conditions in Einstein-Gauss-Bonnet gravity
Properties of -dimensional static wormhole solutions are
investigated in Einstein-Gauss-Bonnet gravity with or without a cosmological
constant . We assume that the spacetime has symmetries corresponding
to the isometries of an -dimensional maximally symmetric space with the
sectional curvature . It is also assumed that the metric is at
least and the -dimensional maximally symmetric subspace is
compact. Depending on the existence or absence of the general relativistic
limit , solutions are classified into general relativistic (GR)
and non-GR branches, respectively, where is the Gauss-Bonnet coupling
constant. We show that a wormhole throat respecting the dominant energy
condition coincides with a branch surface in the GR branch, otherwise the null
energy condition is violated there. In the non-GR branch, it is shown that
there is no wormhole solution for . For the matter field with
zero tangential pressure, it is also shown in the non-GR branch with
and that the dominant energy condition holds at the
wormhole throat if the radius of the throat satisfies some inequality. In the
vacuum case, a fine-tuning of the coupling constants is shown to be necessary
and the radius of a wormhole throat is fixed. Explicit wormhole solutions
respecting the energy conditions in the whole spacetime are obtained in the
vacuum and dust cases with and .Comment: 10 pages, 2 tables; v2, typos corrected, references added; v3,
interpretation of the solution for n=5 in section IV corrected; v4, a very
final version to appear in Physical Review
Bulk scalar emission from a rotating black hole pierced by a tense brane
We study the emission of scalar fields into the bulk from a six-dimensional
rotating black hole pierced by a 3-brane. We determine the angular eigenvalues
in the presence of finite brane tension by using the continued fraction method.
The radial equation is integrated numerically, giving the absorption
probability (graybody factor) in a wider frequency range than in the
preexisting literature. We then compute the power and angular momentum emission
spectra for different values of the rotation parameter and brane tension, and
compare their relative behavior in detail. As is expected from the earlier
result for a nonrotating black hole, the finite brane tension suppresses the
emission rates. As the rotation parameter increases, the power spectra are
reduced at low frequencies due to the smaller Hawking temperature and are
enhanced at high frequencies due to superradiance. The angular momentum spectra
are enhanced over the whole frequency range as the rotation parameter
increases. The spectra and the amounts of energy and angular momentum radiated
away into the bulk are thus determined by the interplay of these effects.Comment: 10 pages, 7 figures; v2: references added; v3: Figs. 4, 5, 6
corrected. Numerical results changed; v4: references added, minor
clarification, accepted for publication in Physical Review
Cosmological rotating black holes in five-dimensional fake supergravity
In recent series of papers, we found an arbitrary dimensional, time-evolving
and spatially-inhomogeneous solutions in Einstein-Maxwell-dilaton gravity with
particular couplings. Similar to the supersymmetric case the solution can be
arbitrarily superposed in spite of non-trivial time-dependence, since the
metric is specified by a set of harmonic functions. When each harmonic has a
single point source at the center, the solution describes a spherically
symmetric black hole with regular Killing horizons and the spacetime approaches
asymptotically to the Friedmann-Lema\^itre-Robertson-Walker (FLRW) cosmology.
We discuss in this paper that in 5-dimensions this equilibrium condition traces
back to the 1st-order "Killing spinor" equation in "fake supergravity" coupled
to arbitrary U(1) gauge fields and scalars. We present a 5-dimensional,
asymptotically FLRW, rotating black-hole solution admitting a nontrivial
"Killing spinor," which is a spinning generalization of our previous solution.
We argue that the solution admits nondegenerate and rotating Killing horizons
in contrast with the supersymmetric solutions. It is shown that the present
pseudo-supersymmetric solution admits closed timelike curves around the central
singularities. When only one harmonic is time-dependent, the solution oxidizes
to 11-dimensions and realizes the dynamically intersecting M2/M2/M2-branes in a
rotating Kasner universe. The Kaluza-Klein type black holes are also discussed.Comment: 24 pages, 2 figures; v2: references added, to appear in PR
Scaling Laws in High-Energy Inverse Compton Scattering. II. Effect of Bulk Motions
We study the inverse Compton scattering of the CMB photons off high-energy
nonthermal electrons. We extend the formalism obtained by the previous paper to
the case where the electrons have non-zero bulk motions with respect to the CMB
frame. Assuming the power-law electron distribution, we find the same scaling
law for the probability distribution function P_{1,K}(s) as P_{1}(s) which
corresponds to the zero bulk motions, where the peak height and peak position
depend only on the power-index parameter. We solved the rate equation
analytically. It is found that the spectral intensity function also has the
same scaling law. The effect of the bulk motions to the spectral intensity
function is found to be small. The present study will be applicable to the
analysis of the X-ray and gamma-ray emission models from various astrophysical
objects with non-zero bulk motions such as radio galaxies and astrophysical
jets.Comment: 10 pages, 3 figures, accepted version by Physical Review
Observation of Conduction Band Satellite of Ni Metal by 3p-3d Resonant Inverse Photoemission Study
Resonant inverse photoemission spectra of Ni metal have been obtained across
the Ni 3 absorption edge. The intensity of Ni 3 band just above Fermi
edge shows asymmetric Fano-like resonance. Satellite structures are found at
about 2.5 and 4.2 eV above Fermi edge, which show resonant enhancement at the
absorption edge. The satellite structures are due to a many-body configuration
interaction and confirms the existence of 3 configuration in the ground
state of Ni metal.Comment: 4 pages, 3 figures, submitted to Physical Review Letter
Ultraviolet television data from the Orbiting Astronomical Observatory. 1: Instrumentation and analysis techniques for the celescope experiment
The celescope instrumentation and data analysis system is described, the major problems encountered during orbital operation are summerized, and a few major problems that were anticipated but did not materialize are listed
Aggregation of SiC-X Grains in Supernova Ejecta
We present a model for the formation of silicon carbide aggregates within the
expanding and cooling supernova remnant. Many SiC-X grains have been found to
be aggregates of smaller crystals which are isotopically homogenous. The
initial condensation of SiC in the ejecta occurs within a interior dense shell
of material which is created by a reverse shock which rebounds from the
core-envelope interface. A subsequent reverse shock accelerates the grains
forward, but the gas drag from the ejecta on the rapidly moving particles
limits their travel distance. By observing the effects of gas drag on the
travel distance of grains, we propose that supernova grain aggregates form from
material that condensed in a highly localized region, which satisfies the
observational evidence of isotopic homogeneity in SiC-X grains.Comment: 9 pages, 5 figures, To be published in the Astrophysical Journa
Analytical Study on the Sunyaev-Zeldovich Effect for Clusters of Galaxies. II. comparison of covariant formalisms
We study a covariant formalism for the Sunyaev-Zeldovich effects developed in
the previous papers by the present authors, and derive analytic expressions for
the redistribution functions in the Thomson approximation. We also explore
another covariant formalism recently developed by Poutanen and Vurm. We show
that the two formalisms are mathematically equivalent in the Thomson
approximation which is fully valid for the cosmic microwave background photon
energies. The present finding will establish a theoretical foundation for the
analysis of the Sunyaev-Zeldovich effects for the clusters of galaxies.Comment: Accepted version, 7 pages, 1 figure, accepted by Physical Review D
for publicatio
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