25,692 research outputs found
Kinks in Time and their Relation to Confinement
The time dependent formation of an electric flux tube (fundamental string) is
reviewed. The main tool used for analysis is the Spacelike brane, which is a
kink in time of the rolling tachyon. Both the S-brane and rolling tachyon are
attempts to extend the D-brane concept to time dependent backgrounds. While
S-branes are similar to Euclidean counterparts of the more familiar timelike
D-branes, S-branes can smoothly change their worldvolume signature from
spacelike to timelike which we interpret as the formation of a topological
defect.Comment: 5 pages, 3 figures. To appear in the Proceedings of Confinement 200
Holographic Duals of Black Holes in Five-dimensional Minimal Supergravity
We examine the dual conformal field theory for extremal charged black holes
in five-dimensional minimal supergravity with 2 independent angular momenta.
The conformal field theory Virasoro algebra, central charge, and temperature
are calculated. Additionally the conformal field theory entropy is calculated
using the Cardy formula and agrees with the Bekenstein-Hawking black hole
entropy. The central charges are directly proportional to the angular momentum
components of the black hole. In five and higher dimensions, rotations of the
spacetime correspond to rotations of the central charges leading to an apparent
symmetry relating the conformal field theories dual to each black hole. A
rotationally invariant central charge, which is proportional to the total
angular momentum, is used to discuss the supersymmetric BMPV black hole limits.Comment: inaccurate descriptions are clarifie
Schrodinger formalism, black hole horizons and singularity behavior
The Gauss-Codazzi method is used to discuss the gravitational collapse of a
charged Reisner-Nordstr\"om domain wall. We solve the classical equations of
motion of a thin charged shell moving under the influence of its own
gravitational field and show that a form of cosmic censorship applies. If the
charge of the collapsing shell is greater than its mass, then the collapse does
not form a black hole. Instead, after reaching some minimal radius, the shell
bounces back. The Schrodinger canonical formalism is used to quantize the
motion of the charged shell. The limits near the horizon and near the
singularity are explored. Near the horizon, the Schrodinger equation describing
evolution of the collapsing shell takes the form of the massive wave equation
with a position dependent mass. The outgoing and incoming modes of the solution
are related by the Bogolubov transformation which precisely gives the Hawking
temperature. Near the classical singularity, the Schrodinger equation becomes
non-local, but the wave function describing the system is non-singular. This
indicates that while quantum effects may be able to remove the classical
singularity, it may also introduce some new effects.Comment: 10 pages; v2 added references and further comment on singularity
behavior, version to appear in PR
Oxygen isotope geochemistry of the second HSDP core
Oxygen isotope ratios were measured in olivine phenocrysts (~1 mm diameter), olivine microphenocrysts (generally ~100–200 µm diameter), glass, and/or matrix from 89 samples collected from depths down to 3079.7 m in the second, and main, HSDP core (HSDP-2). Olivine phenocrysts from 11 samples from Mauna Loa and 34 samples from the submarine section of Mauna Kea volcano have delta18O values that are similar to one another (5.11 ± 0.10‰, 1sigma, for Mauna Loa; 5.01 ± 0.07‰, for submarine Mauna Kea) and within the range of values typical of olivines from oceanic basalts (delta18O of ~5.0 to 5.2‰). In contrast, delta18O values of olivine phenocrysts from 20 samples taken from the subaerial section of Mauna Kea volcano (278 to 1037 mbsl) average 4.79 ± 0.13‰. Microphenocrysts in both the subaerial (n = 2) and submarine (n = 24) sections of Mauna Kea are on average ~0.2‰ lower in delta18O than phenocrysts within the same stratigraphic interval; those in submarine Mauna Kea lavas have an average delta18O of 4.83 ± 0.11‰. Microphenocrysts in submarine Mauna Kea lavas and phencrysts in Mauna Loa lavas are the only population of olivines considered in this study that are typically in oxygen isotope exchange equilibrium with coexisting glass or groundmass. These data confirm the previous observation that the stratigraphic boundary between Mauna Loa and Mauna Kea lavas defines a shift from “normal” to unusually low delta18O values. Significantly, they also document that the distinctive 18O-depleted character of subaerial Mauna Kea lavas is absent in phenocrysts of submarine Mauna Kea lavas. Several lines of evidence suggest that little if any of the observed variations in delta18O can be attributed to subsolidus alteration or equilibrium fractionations accompanying partial melting or crystallization. Instead, they reflect variable proportions of an 18O-depleted source component or contaminant from the lithosphere and/or volcanic edifice that is absent in or only a trace constituent of subaerial Mauna Loa lavas, a minor component of submarine Mauna Kea lavas, and a major component of subaerial Mauna Kea lavas. Relationships between the delta18O of phenocrysts, microphenocrysts, and glass or groundmass indicate that this component (when present) was added over the course of crystallization-differentiation. This process must have taken place in the lithosphere and most likely at depths of between ~5 and 15 km. We conclude that the low-delta18O component is either a contaminant from the volcanic edifice that was sampled in increasingly greater proportions as the volcano drifted off the center of the Hawaiian plume or a partial melt of low-delta18O, hydrothermally altered perdotites in the shallow Pacific lithosphere that increasingly contributed to Mauna Kea lavas near end of the volcano's shield building stage. The first of these alternatives is favored by the difference in delta18O between subaerial and submarine Mauna Kea lavas, whereas the second is favored by systematic differences in radiogenic and trace element composition between higher and lower delta18O lavas
De Sitter Bounces
By analytically continuing recently-found instantons, we construct
time-dependent solutions of Einstein-Maxwell de Sitter gravity which smoothly
bounce between two de Sitter phases. These deformations of de Sitter space
undergo several stages in their time evolution. Four and five-dimensional de
Sitter bounces can be lifted to non-singular time-dependent solutions of
M-theory.Comment: Latex, 18 pages, 5 figure
Modelling the spring ozone maximum and the interhemispheric asymmetry in the remote marine boundary layer 1. Comparison with surface and ozonesonde measurements
Here we report a modelling study of the spring ozone maximum and its
interhemispheric asymmetry in the remote marine boundary layer (MBL). The
modelled results are examined at the surface and on a series of time-height
cross sections at several locations spread over the Atlantic, the Indian, and
the Pacific Oceans. Comparison of model with surface measurements at remote MBL
stations indicate a close agreement. The most striking feature of the
hemispheric spring ozone maximum in the MBL can be most easily identified at
the NH sites of Westman Island, Bermuda, and Mauna Loa, and at the SH site of
Samoa. Modelled ozone vertical distributions in the troposphere are compared
with ozone profiles. For the Atlantic and the Indian sites, the model generally
produces a hemispheric spring ozone maximum close to those of the measurements.
The model also produces a spring ozone maximum in the northeastern and tropical
north Pacific close to those measurements, and at sites in the NH high
latitudes. The good agreement between model and measurements indicate that the
model can reproduce the proposed mechanisms responsible for producing the
spring ozone maximum in these regions of the MBL, lending confidence in the use
of the model to investigate MBL ozone chemistry (see part 2 and part 3). The
spring ozone maximum in the tropical central south Pacific and eastern
equatorial Pacific are less well reproduced by the model, indicating that both
the transport of precursors from biomass burning emissions taking place
in southeastern Asia, Australia, Oceania, southern Africa, and South America
are not well represented in the model in these regions. Overall, the model
produces a better simulation at sites where the stratosphere and biomass
burning emissions are the major contributors.Comment: 24 pages, 8 figure
- …