58 research outputs found
Perturbations of Spacetime around a Stationary Rotating Cosmic String
We consider the metric perturbations around a stationary rotating Nambu-Goto
string in Minkowski spacetime. By solving the linearized Einstein equations, we
study the effects of azimuthal frame-dragging around the rotation axis and
linear frame-dragging along the rotation axis, the Newtonian logarithmic
potential, and the angular deficit around the string as the potential mode. We
also investigate gravitational waves propagating off the string and propagating
along the string, and show that the stationary rotating string emits
gravitational waves toward the directions specified by discrete angles from the
rotation axis. Waveforms, polarizations, and amplitudes which depend on the
direction are shown explicitly.Comment: 30 pages, 6 figures; Minor corrections, references added, published
version in Physical Review
Classification of Cohomogeneity One Strings
We define the cohomogeneity one string, string with continuous symmetries, as
its world surface is tangent to a Killing vector field of a target space. We
classify the Killing vector fields by an equivalence relation using isometries
of the target space. We find that the equivalence classes of Killing vectors in
Minkowski spacetime are partitioned into seven families. It is clarified that
there exist seven types of strings with spacelike symmetries and four types of
strings with timelike symmetries, stationary strings.Comment: 8 page
Ontology Mapping of PATO to YATO for the improvement of interoperability of quality description
To facilitate broad interoperability for phenotype information between different ontological frameworks, we developed a reference ontology, PATO2YATO_Quality, with the careful mapping of terms of PATO which is a quality ontology commonly used for biological phenotype annotation to the latest top-level ontology, YATO, which represents advanced modeling of quality-related concepts. As a result, YATO framework enabled to describe changes of phenotypic qualities along the courses of time in ontologically correct way and sophisticated classification and representation of interrelationships among quality-related concepts to provide fully integration of qualitative values and quantitative values obtained from phenotyping experiments and advanced representation of more detailed quality description. Thus, PATO2YATO_Quality will contribute to advanced integration of phenotypic qualities
Strings in five-dimensional anti-de Sitter space with a symmetry
The equation of motion of an extended object in spacetime reduces to an
ordinary differential equation in the presence of symmetry. By properly
defining of the symmetry with notion of cohomogeneity, we discuss the method
for classifying all these extended objects. We carry out the classification for
the strings in the five-dimensional anti-de Sitter space by the effective use
of the local isomorphism between \SO(4,2) and \SU(2,2). We present a
general method for solving the trajectory of the Nambu-Goto string and apply to
a case obtained by the classification, thereby find a new solution which has
properties unique to odd-dimensional anti-de Sitter spaces. The geometry of the
solution is analized and found to be a timelike helicoid-like surface
Can inhomogeneties accelerate the cosmic volume expansion?
If expanding and contracting regions coexist in the universe, the speed of
the cosmic volume expansion can be accelerated. We construct simple
inhomogeneous dust-filled universe models in which the speed of the cosmic
volume expansion is accelerated for finite periods. These models are
constructed by removing spherical domains from the Einstein-de Sitter universe
and filling each domain with a Lemaitre-Tolman-Bondi dust sphere possessing the
same gravitational mass as the removed region. This represents an exact
solution of the Einstein equations. We find that acceleration of the cosmic
volume expansion is realized in some cases when the size of the contracting
region is comparable to the horizon radius of the Einstein-de Sitter universe
though this model is very different from the universe observed today. This
result implies that non-linear general relativistic effects of inhomogeneities
are very important to realize the acceleration of the cosmic volume expansion.Comment: 12 pages,5 figures. version published in Progress of Theoretical
Physic
Stationary Rotating Strings as Relativistic Particle Mechanics
Stationary rotating strings can be viewed as geodesic motions in appropriate
metrics on a two-dimensional space. We obtain all solutions describing
stationary rotating strings in flat spacetime as an application. These rotating
strings have infinite length with various wiggly shapes. Averaged value of the
string energy, the angular momentum and the linear momentum along the string
are discussed.Comment: 20pages, 7 figure
Exactly solvable strings in Minkowski spacetime
We study the integrability of the equations of motion for the Nambu-Goto
strings with a cohomogeneity-one symmetry in Minkowski spacetime. A
cohomogeneity-one string has a world surface which is tangent to a Killing
vector field. By virtue of the Killing vector, the equations of motion can be
reduced to the geodesic equation in the orbit space. Cohomogeneity-one strings
are classified into seven classes (Types I to VII). We investigate the
integrability of the geodesic equations for all the classes and find that the
geodesic equations are integrable. For Types I to VI, the integrability comes
from the existence of Killing vectors on the orbit space which are the
projections of Killing vectors on Minkowski spacetime. For Type VII, the
integrability is related to a projected Killing vector and a nontrivial Killing
tensor on the orbit space. We also find that the geodesic equations of all
types are exactly solvable, and show the solutions.Comment: 11 pages, a reference added, some points clarifie
Lensing Effects on Gravitational Waves in a Clumpy Universe -Effects of Inhomogeneity on the Distance-Redshift Relation-
The distance-redshift relation determined by means of gravitational waves in
the clumpy universe is simulated numerically by taking into account the effects
of gravitational lensing. It is assumed that all of the matter in the universe
takes the form of randomly distributed point masses, each of which has the
identical mass . Calculations are carried out in two extreme cases:
and , where denotes the
wavelength of gravitational waves. In the first case, the distance-redshift
relation for the fully homogeneous and isotropic universe is reproduced with a
small distance dispersion, whereas in the second case, the distance dispersion
is larger. This result suggests that we might obtain information about the
typical mass of lens objects through the distance-redshift relation gleaned
through observation of gravitational waves of various wavelengths. In this
paper, we show how to set limitations on the mass through the observation
of gravitational waves in the clumpy universe model described above.Comment: 35 pages, 21 figures, ApJ accepted versio
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