701 research outputs found
Scalar wave propagation in topological black hole backgrounds
We consider the evolution of a scalar field coupled to curvature in
topological black hole spacetimes. We solve numerically the scalar wave
equation with different curvature-coupling constant and show that a rich
spectrum of wave propagation is revealed when is introduced. Relations
between quasinormal modes and the size of different topological black holes
have also been investigated.Comment: 26 pages, 18 figure
Pair of accelerated black holes in a de Sitter background: the dS C-metric
Following the work of Kinnersley and Walker for flat spacetimes, we have
analyzed the anti-de Sitter C-metric in a previous paper. In the de Sitter
case, Podolsky and Griffiths have established that the de Sitter C-metric (dS
C-metric) found by Plebanski and Demianski describes a pair of accelerated
black holes in the dS background with the acceleration being provided (in
addition to the cosmological constant) by a strut that pushes away the two
black holes or, alternatively, by a string that pulls them. We extend their
analysis mainly in four directions. First, we draw the Carter-Penrose diagrams
of the massless uncharged dS C-metric, of the massive uncharged dS C-metric and
of the massive charged dS C-metric. These diagrams allow us to clearly identify
the presence of two dS black holes and to conclude that they cannot interact
gravitationally. Second, we revisit the embedding of the dS C-metric in the 5D
Minkowski spacetime and we represent the motion of the dS C-metric origin in
the dS 4-hyperboloid as well as the localization of the strut. Third, we
comment on the physical properties of the strut that connects the two black
holes. Finally, we find the range of parameters that correspond to non-extreme
black holes, extreme black holes, and naked particles.Comment: 11 pages, 11 figures (RevTeX4). Published version: references adde
Interior Structure of a Charged Spinning Black Hole in -Dimensions
The phenomenon of mass inflation is shown to occur for a rotating black hole.
We demonstrate this feature in dimensions by extending the charged
spinning BTZ black hole to Vaidya form. We find that the mass function diverges
in a manner quantitatively similar to its static counterparts in ,
and dimensions.Comment: 5 pages, 2 figures (appended as postscript files), WATPHYS-TH94/0
Uniformly Accelerated Charge in a Quantum Field: From Radiation Reaction to Unruh Effect
We present a stochastic theory for the nonequilibrium dynamics of charges
moving in a quantum scalar field based on the worldline influence functional
and the close-time-path (CTP or in-in) coarse-grained effective action method.
We summarize (1) the steps leading to a derivation of a modified
Abraham-Lorentz-Dirac equation whose solutions describe a causal semiclassical
theory free of runaway solutions and without pre-acceleration patholigies, and
(2) the transformation to a stochastic effective action which generates
Abraham-Lorentz-Dirac-Langevin equations depicting the fluctuations of a
particle's worldline around its semiclassical trajectory. We point out the
misconceptions in trying to directly relate radiation reaction to vacuum
fluctuations, and discuss how, in the framework that we have developed, an
array of phenomena, from classical radiation and radiation reaction to the
Unruh effect, are interrelated to each other as manifestations at the
classical, stochastic and quantum levels. Using this method we give a
derivation of the Unruh effect for the spacetime worldline coordinates of an
accelerating charge. Our stochastic particle-field model, which was inspired by
earlier work in cosmological backreaction, can be used as an analog to the
black hole backreaction problem describing the stochastic dynamics of a black
hole event horizon.Comment: Invited talk given by BLH at the International Assembly on
Relativistic Dynamics (IARD), June 2004, Saas Fee, Switzerland. 19 pages, 1
figur
Expanding and Collapsing Scalar Field Thin Shell
This paper deals with the dynamics of scalar field thin shell in the
Reissner-Nordstrm geometry. The Israel junction conditions between
Reissner-Nordstrm spacetimes are derived, which lead to the equation
of motion of scalar field shell and Klien-Gordon equation. These equations are
solved numerically by taking scalar field model with the quadratic scalar
potential. It is found that solution represents the expanding and collapsing
scalar field shell. For the better understanding of this problem, we
investigate the case of massless scalar field (by taking the scalar field
potential zero). Also, we evaluate the scalar field potential when is an
explicit function of . We conclude that both massless as well as massive
scalar field shell can expand to infinity at constant rate or collapse to zero
size forming a curvature singularity or bounce under suitable conditions.Comment: 15 pages, 11 figure
The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets
This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics
Charged AdS Black Holes and Catastrophic Holography
We compute the properties of a class of charged black holes in anti-de Sitter
space-time, in diverse dimensions. These black holes are solutions of
consistent Einstein-Maxwell truncations of gauged supergravities, which are
shown to arise from the inclusion of rotation in the transverse space. We
uncover rich thermodynamic phase structures for these systems, which display
classic critical phenomena, including structures isomorphic to the van der
Waals-Maxwell liquid-gas system. In that case, the phases are controlled by the
universal `cusp' and `swallowtail' shapes familiar from catastrophe theory. All
of the thermodynamics is consistent with field theory interpretations via
holography, where the dual field theories can sometimes be found on the world
volumes of coincident rotating branes.Comment: 19 pages, revtex, psfig, 6 multicomponent figures, typos, references
and a few remarks have been repaired, and adde
Height and risk of death among men and women: aetiological implications of associations with cardiorespiratory disease and cancer mortality
OBJECTIVES: Height is inversely associated with cardiovascular disease mortality risk and has shown variable associations with cancer incidence and mortality. The interpretation of findings from previous studies has been constrained by data limitations. Associations between height and specific causes of death were investigated in a large general population cohort of men and women from the West of Scotland.
DESIGN: Prospective observational study.
SETTING: Renfrew and Paisley, in the West of Scotland.
SUBJECTS: 7052 men and 8354 women aged 45-64 were recruited into a study in Renfrew and Paisley, in the West of Scotland, between 1972 and 1976. Detailed assessments of cardiovascular disease risk factors, morbidity and socioeconomic circumstances were made at baseline.
MAIN OUTCOME MEASURES: Deaths during 20 years of follow up classified into specific causes.
RESULTS: Over the follow up period 3347 men and 2638 women died. Height is inversely associated with all cause, coronary heart disease, stroke, and respiratory disease mortality among men and women. Adjustment for socioeconomic position and cardiovascular risk factors had little influence on these associations. Height is strongly associated with forced expiratory volume in one second (FEV1) and adjustment for FEV1 considerably attenuated the association between height and cardiorespiratory mortality. Smoking related cancer mortality is not associated with height. The risk of deaths from cancer unrelated to smoking tended to increase with height, particularly for haematopoietic, colorectal and prostate cancers. Stomach cancer mortality was inversely associated with height. Adjustment for socioeconomic position had little influence on these associations.
CONCLUSION: Height serves partly as an indicator of socioeconomic circumstances and nutritional status in childhood and this may underlie the inverse associations between height and adulthood cardiorespiratory mortality. Much of the association between height and cardiorespiratory mortality was accounted for by lung function, which is also partly determined by exposures acting in childhood. The inverse association between height and stomach cancer mortality probably reflects Helicobacter pylori infection in childhood resulting inor being associated withshorter height. The positive associations between height and several cancers unrelated to smoking could reflect the influence of calorie intake during childhood on the risk of these cancers
Statistical Theory of Spin Relaxation and Diffusion in Solids
A comprehensive theoretical description is given for the spin relaxation and
diffusion in solids. The formulation is made in a general
statistical-mechanical way. The method of the nonequilibrium statistical
operator (NSO) developed by D. N. Zubarev is employed to analyze a relaxation
dynamics of a spin subsystem. Perturbation of this subsystem in solids may
produce a nonequilibrium state which is then relaxed to an equilibrium state
due to the interaction between the particles or with a thermal bath (lattice).
The generalized kinetic equations were derived previously for a system weakly
coupled to a thermal bath to elucidate the nature of transport and relaxation
processes. In this paper, these results are used to describe the relaxation and
diffusion of nuclear spins in solids. The aim is to formulate a successive and
coherent microscopic description of the nuclear magnetic relaxation and
diffusion in solids. The nuclear spin-lattice relaxation is considered and the
Gorter relation is derived. As an example, a theory of spin diffusion of the
nuclear magnetic moment in dilute alloys (like Cu-Mn) is developed. It is shown
that due to the dipolar interaction between host nuclear spins and impurity
spins, a nonuniform distribution in the host nuclear spin system will occur and
consequently the macroscopic relaxation time will be strongly determined by the
spin diffusion. The explicit expressions for the relaxation time in certain
physically relevant cases are given.Comment: 41 pages, 119 Refs. Corrected typos, added reference
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