511 research outputs found
3-D General Relativistic MHD Simulations of Generating Jets
We have performed a first fully 3-D GRMHD simulation with Schwarzschild black
hole with a free falling corona. The initial simulation results show that a jet
is created as in previous axisymmetric simulations. However, the time to
generate the jet is longer than in the 2-D simulations. We expect that due to
the additional azimuthal dimension the dynamics of jet formation can be
modified.Comment: 4 pages Proc. Oxford Radio Galaxy Workshop ed. R. Laing & K. Blundell
(San Francisco: PASP) in press (revised
Six-dimensional localized black holes: numerical solutions
To test the strong-gravity regime in Randall-Sundrum braneworlds, we consider
black holes bound to a brane. In a previous paper, we studied numerical
solutions of localized black holes whose horizon radii are smaller than the AdS
curvature radius. In this paper, we improve the numerical method and discuss
properties of the six dimensional (6D) localized black holes whose horizon
radii are larger than the AdS curvature radius. At a horizon temperature
, the thermodynamics of the localized black
hole undergo a transition with its character changing from a 6D Schwarzschild
black hole type to a 6D black string type. The specific heat of the localized
black holes is negative, and the entropy is greater than or nearly equal to
that of the 6D black strings with the same thermodynamic mass. The large
localized black holes show flattened horizon geometries, and the intrinsic
curvature of the horizon four-geometry becomes negative near the brane. Our
results indicate that the recovery mechanism of lower-dimensional Einstein
gravity on the brane works even in the presence of the black holes.Comment: 17 pages, 9 figures, RevTeX4, typos correcte
Small localized black holes in a braneworld: Formulation and numerical method
No realistic black holes localized on a 3-brane in the Randall-Sundrum
infinite braneworld have been found so far. The problem of finding a static
black hole solution is reduced to a boundary value problem. We solve it by
means of a numerical method, and show numerical examples of a localized black
hole whose horizon radius is small compared to the bulk curvature scale. The
sequence of small localized black holes exhibits a smooth transition from a
five-dimensional Schwarzschild black hole, which is a solution in the limit of
small horizon radius. The localized black hole tends to flatten as its horizon
radius increases. However, it becomes difficult to find black hole solutions as
its horizon radius increases.Comment: RevTeX, 13 pages, 6 figures, references corrected, typos corrected;
to appear in Phys.Rev.
Strong Brane Gravity and the Radion at Low Energies
For the 2-brane Randall-Sundrum model, we calculate the bulk geometry for
strong gravity, in the low matter density regime, for slowly varying matter
sources. This is relevant for astrophysical or cosmological applications. The
warped compactification means the radion can not be written as a homogeneous
mode in the orbifold coordinate, and we introduce it by extending the
coordinate patch approach of the linear theory to the non-linear case. The
negative tension brane is taken to be in vacuum. For conformally invariant
matter on the positive tension brane, we solve the bulk geometry as a
derivative expansion, formally summing the `Kaluza-Klein' contributions to all
orders. For general matter we compute the Einstein equations to leading order,
finding a scalar-tensor theory with ,
and geometrically interpret the radion. We comment that this radion scalar may
become large in the context of strong gravity with low density matter.
Equations of state allowing to be negative, can exhibit behavior
where the matter decreases the distance between the 2 branes, which we
illustrate numerically for static star solutions using an incompressible fluid.
For increasing stellar density, the branes become close before the upper mass
limit, but after violation of the dominant energy condition. This raises the
interesting question of whether astrophysically reasonable matter, and initial
data, could cause branes to collide at low energy, such as in dynamical
collapse.Comment: 24 pages, 3 figure
Black hole production in tachyonic preheating
We present fully non-linear simulations of a self-interacting scalar field in
the early universe undergoing tachyonic preheating. We find that density
perturbations on sub-horizon scales which are amplified by tachyonic
instability maintain long range correlations even during the succeeding
parametric resonance, in contrast to the standard models of preheating
dominated by parametric resonance. As a result the final spectrum exhibits
memory and is not universal in shape. We find that throughout the subsequent
era of parametric resonance the equation of state of the universe is almost
dust-like, hence the Jeans wavelength is much smaller than the horizon scale.
If our 2D simulations are accurate reflections of the situation in 3D, then
there are wide regions of parameter space ruled out by over-production of black
holes. It is likely however that realistic parameter values, consistent with
COBE/WMAP normalisation, are safetly outside this black hole over-production
region.Comment: 6pages, 7figures, figures correcte
Are black holes over-produced during preheating?
We provide a simple but robust argument that primordial black hole (PBH)
production generically does {\em not} exceed astrophysical bounds during the
resonant preheating phase after inflation. This conclusion is supported by
fully nonlinear lattice simulations of various models in two and three
dimensions which include rescattering but neglect metric perturbations. We
examine the degree to which preheating amplifies density perturbations at the
Hubble scale and show that at the end of the parametric resonance, power
spectra are universal, with no memory of the power spectrum at the end of
inflation. In addition we show how the probability distribution of density
perturbations changes from exponential on very small scales to Gaussian when
smoothed over the Hubble scale -- the crucial length for studies of primordial
black hole formation -- hence justifying the standard assumption of
Gaussianity.Comment: 12 pages, 8 figures, revtex, added references for section
Left-right asymmetric expression of dpp in the mantle of gastropods correlates with asymmetric shell coiling
This is the final version of the article. Available from BMC via the DOI in this record.BACKGROUND: Various shapes of gastropod shells have evolved ever since the Cambrian. Although theoretical analyses of morphogenesis exist, the molecular basis of shell development remains unclear. We compared expression patterns of the decapentaplegic (dpp) gene in the shell gland and mantle tissues at various developmental stages between coiled-shell and non-coiled-shell gastropods. RESULTS: We analyzed the expression patterns of dpp for the two limpets Patella vulgata and Nipponacmea fuscoviridis, and for the dextral wild-type and sinistral mutant lineage of the pond snail Lymnaea stagnalis. The limpets had symmetric expression patterns of dpp throughout ontogeny, whereas in the pond snail, the results indicated asymmetric and mirror image patterns between the dextral and sinistral lineages. CONCLUSION: We hypothesize that Dpp induces mantle expansion, and the presence of a left/right asymmetric gradient of the Dpp protein causes the formation of a coiled shell. Our results provide a molecular explanation for shell, coiling including new insights into expression patterns in post-embryonic development, which should aid in understanding how various shell shapes are formed and have evolved in the gastropods.This study was supported by the JSPS Grants-in-Aid for Scientific Research 15104009
A General Relativistic Magnetohydrodynamics Simulation of Jet Formation
We have performed a fully three-dimensional general relativistic
magnetohydrodynamic (GRMHD) simulation of jet formation from a thin accretion
disk around a Schwarzschild black hole with a free-falling corona. The initial
simulation results show that a bipolar jet (velocity ) is created as
shown by previous two-dimensional axisymmetric simulations with mirror symmetry
at the equator. The 3-D simulation ran over one hundred light-crossing time
units ( where ) which is
considerably longer than the previous simulations. We show that the jet is
initially formed as predicted due in part to magnetic pressure from the
twisting the initially uniform magnetic field and from gas pressure associated
with shock formation in the region around . At later times,
the accretion disk becomes thick and the jet fades resulting in a wind that is
ejected from the surface of the thickened (torus-like) disk. It should be noted
that no streaming matter from a donor is included at the outer boundary in the
simulation (an isolated black hole not binary black hole). The wind flows
outwards with a wider angle than the initial jet. The widening of the jet is
consistent with the outward moving torsional Alfv\'{e}n waves (TAWs). This
evolution of disk-jet coupling suggests that the jet fades with a thickened
accretion disk due to the lack of streaming material from an accompanying star.Comment: 27 pages, 8 figures, revised and accepted to ApJ (figures with better
resolution: http://gammaray.nsstc.nasa.gov/~nishikawa/schb1.pdf
Primordial gravitational waves in inflationary braneworld
We study primordial gravitational waves from inflation in Randall-Sundrum
braneworld model. The effect of small change of the Hubble parameter during
inflation is investigated using a toy model given by connecting two de Sitter
branes. We analyze the power spectrum of final zero-mode gravitons, which is
generated from the vacuum fluctuations of both initial Kaluza-Klein modes and
zero-mode. The amplitude of fluctuations is confirmed to agree with the
four-dimensional one at low energies, whereas it is enhanced due to the
normalization factor of zero-mode at high energies. We show that the
five-dimensional spectrum can be well approximated by applying a simple mapping
to the four-dimensional fluctuation amplitude.Comment: 16 pages, 4 figures, typos correcte
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