363 research outputs found
Creation of a black hole pair with a domain wall
We study the creation of a black hole (BH) pair separated by a domain wall,
in the presence of a cosmological constant. We construct the solution
representing a BH pair with a domain wall and compute the Euclidean action to
evaluate the probability of the pair creation in the background with a
preexisting domain wall. The BHs can be either neutral or magnetically charged
ones. We compare the results of the charged case with those of the neutral case
with the same cosmological constant. We find that the production rate of a
charged BH pair is always suppressed in comparison with that of the neutral one
in both four and five dimensions, irrespective of the sign of the cosmological
constant. The Euclidean action is equal to the minus of the entropy. Since the
horizon area of a BH is decreased as the magnitude of its charge is increased
in general, the decreasing creation rate can be understood in terms of the
increasing charge. We obtain the explicit confirmation on the relation between
the pair creation rate of the charged BHs and the area of horizons in both the
four- and five-dimensional cases in the presence of a cosmological constant.
The singularity of the domain wall universe with charged BHs, as distinct from
that with neutral BHs, can be avoided.Comment: 23 pages, 11 figures, Some typos corrected and references added with
respect to the published versio
The false vacuum bubble nucleation due to a nonminimally coupled scalar field
We study the possibility of forming the false vacuum bubble nucleated within
the true vacuum background via the true-to-false vacuum phase transition in
curved spacetime. We consider a semiclassical Euclidean bubble in the Einstein
theory of gravity with a nonminimally coupled scalar field. In this paper we
present the numerical computations as well as the approximate analytical
computations. We mention the evolution of the false vacuum bubble after
nucleation.Comment: 23 pages, 12 figures, References added, minor correctio
A Holographic Model of Strange Metals
We give a review on our recent work arXiv:1006.0779 [hep-th] and
arXiv:1006.1719 [hep-th], in which properties of holographic strange metals
were investigated. The background is chosen to be anisotropic scaling solution
in Einstein-Maxwell-Dilaton theory with a Liouville potential. The effects of
bulk Maxwell field, an extra U(1) gauge field and probe D-branes on the DC
conductivity, the DC Hall conductivity and the AC conductivity are extensively
analyzed. We classify behaviors of the conductivities according to the
parameter ranges in the bulk theory and characterize conditions when the
holographic results can reproduce experimental data.Comment: 34 pages, 15 figures, minor correction
Particle Probe of Horava-Lifshitz Gravity
Kehagias-Sfetsos black hole in Ho\v{r}ava-Lifshitz gravity is probed through
particle geodesics. Gravitational force of KS black hole becomes weaker than
that of Schwarzschild around horizon and interior space. Particles can be
always scattered or trapped in new closed orbits, unlike those falling forever
in Schwarzschild black. The properties of null and timelike geodesics are
classified with values of coupling constants. The precession rates of the
orbits are evaluated. The time trajectories are also classified under different
values of coupling constants for both null and timelike geodesics. Physical
phenomena that may be observable are discussed.Comment: 10 pages, 8 figure
Regeneration Ecology of Chrysopogon aucheri and Cymbopogon jwarancusa in Grasslands of Upland Balochistan , Pakistan
Field experiments were conducted to investigate the seed attributes, movements and fates of dispersal units, and seedling establishment of Chrysopogon aucheri and Cymbopogon jwarancusa in a representative grassland ecosystem in upland Balochistan, Pakistan.
Cymbopogon jwarancusa had more filled and viable caryopses than Chrysopogon aucheri. Seeds (spikelets) of both species had similar morphological features. Chrysopogon aucheri had one dispersal unit, a triplet spikelet. Cymbopogon jwarancusa had four types of dispersal units: a paired spikelet, a partial raceme, an entire raceme, and a partial inflorescence comprised of two racemes.
Paired spikelets and partial racemes of Cymbopogon jwarancusa had greater mean dispersal distances (94 and 101 cm) from the edge of the basal crown of marked plants to the ground surface than triplet spikelets of Chrysopogon aucheri (79 cm). Spikelets of Cymbopogon jwarancusa and Chrysopogon aucheri moved mean distances of 26 and 32 cm, respectively, on the ground surface before becoming trapped in a microhabitat. The mean angle of dispersal for both species was toward the northeast, according to the prevailing wind direction. An ant (Tica verona) was the only detected seed (spikelet) predator for Chrysopogon aucheri. Both species had a weakly persistent soil seed bank, with higher amounts of seeds found under plant canopies compared to open interspaces.
The recruitment of Chrysopogon aucheri and Cymbopogon jwarancusa seedlings from the natural seed bank was monitored in seven different microhabitats under natural and above-normal precipitation regimes . Above-normal precipitation increased seedling recruitment for both species in all microhabitats. Cymbopogon jwarancusa had higher seedling densities than Chrysopogon auchfiri. Seedling survival and tiller development for both species were greatest in the gravel microhabitat in the natural precipitation treatment. Monsoon rains in late July enhanced emergence of both species from recently dispersed seeds but emerged seedlings did not survive to the end of the growing season.
The field studies indicate that Cymbopogon jwarancusa has a greater regeneration potential than Chrysopogon aucheri in this grassland ecosystem in upland Balochistan. It may be difficult to increase the composition of Chrysopogon aucheri, the more desirable species in these grasslands, when using management techniques that rely on natural regeneration
Layer-by-Layer Assembled Nanowire Networks Enable Graph Theoretical Design of Multifunctional Coatings
Multifunctional coatings are central for information, biomedical,
transportation and energy technologies. These coatings must possess
hard-to-attain properties and be scalable, adaptable, and sustainable, which
makes layer-by-layer assembly (LBL) of nanomaterials uniquely suitable for
these technologies. What remains largely unexplored is that LBL enables
computational methodologies for structural design of these composites.
Utilizing silver nanowires (NWs), we develop and validate a graph theoretical
(GT) description of their LBL composites. GT successfully describes the
multilayer structure with nonrandom disorder and enables simultaneous rapid
assessment of several properties of electrical conductivity, electromagnetic
transparency, and anisotropy. GT models for property assessment can be rapidly
validated due to (1) quasi-2D confinement of NWs and (2) accurate microscopy
data for stochastic organization of the NW networks. We finally show that
spray-assisted LBL offers direct translation of the GT-based design of
composite coatings to additive, scalable manufacturing of drone wings with
straightforward extensions to other technologies
Semiclassical strings in AdS(3) X S^2
In this paper, we investigate the semiclassical strings in AdS(3)XS^2, in
which the string configuration of AdS(3) is classified to three cases depending
on the parameters. Each of these has a different anomalous dimension
proportional to logS, S^(1/3) and S, where S is a angular momentum on AdS(3).
Further we generalize the dispersion relations for various string configuration
on AdS(3)XS^2.Comment: 15 pages, added reference
The vacuum bubbles in de Sitter background and black hole pair creation
We study the possible types of the nucleation of vacuum bubbles. We classify
vacuum bubbles in de Sitter background and present some numerical solutions.
The thin-wall approximation is employed to obtain the nucleation rate and the
radius of vacuum bubbles. With careful analysis we confirm that Parke's formula
is also applicable to the large true vacuum bubbles. The nucleation of the
false vacuum bubble in de Sitter background is also evaluated. The tunneling
process in the potential with degenerate vacua is analyzed as the limiting
cases of the large true vacuum bubble and false vacuum bubble. Next, we
consider the pair creation of black holes in the background of bubble
solutions. We obtain static bubble wall solutions of junction equation with
black hole pair. The masses of created black holes are uniquely determined by
the cosmological constant and surface tension on the wall. Finally, we obtain
the rate of pair creation of black holes.Comment: 3 figures, minor including errors and typos corrected, and refs.
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Anyonic physical observables and spin phase transition
The quantization of charged matter system coupled to Chern-Simons gauge
fields is analyzed in a covariant gauge fixing, and gauge invariant physical
anyon operators satisfying fractional statistics are constructed in a symmetric
phase, based on Dirac's recipe performed on QED. This method provides us a
definite way of identifying physical spectrums free from gauge ambiguity and
constructing physical anyon operators under a covariant gauge fixing. We then
analyze the statistical spin phase transition in a symmetry-broken phase and
show that the Higgs mechanism transmutes an anyon satisfying fractional
statistics into a canonical boson, a spin 0 Higgs boson or a topologically
massive photon.Comment: 14 pages, added references, a few improvement
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