1,780 research outputs found
Non-Perturbative Particle Dynamics
We construct a non-perturbative, single-valued solution for the metric and
the motion of two interacting particles in ()-Gravity, by using a Coulomb
gauge of conformal type. The method provides the mapping from multivalued (
minkowskian ) coordinates to single-valued ones, which solves the non-abelian
monodromies due to particles's momenta and can be applied also to the general
N-body case.Comment: 11 pages, LaTeX, no figure
América Latina como una sociedad de colonización blanca
La historia de América Latina en el siglo xix, caracterizada por la europeización, inmigración y exterminio, sugiere que el continente se puede clasificar perfectamente en la categoría de colonialismo de establecimiento (settler colonialism), una noción usualmente utilizada para describir a las colonias de inmigrantes blancos Provenientes de imperios europeos distintos a los de España y Portugal. Mientras los últimos años de imperio y los primeros días de las repúblicas fueron testigos del esfuerzo por incluir a las poblaciones indígenas como ciudadanas, las élites racistas blancas en el siglo posterior a la independencia se esforzaron por importar inmigrantes europeos para evitar que la población no blanca participara en el poder. El deseado blanqueamiento de la población fue pocas veces exitoso, pero el peso de la inmigración blanca ayudó a crear una sociedad, en el siglo xx, que ignoró a las poblaciones indígenas, hasta los estallidos populares de los años recientes
Self-Gravitating Strings In 2+1 Dimensions
We present a family of classical spacetimes in 2+1 dimensions. Such a
spacetime is produced by a Nambu-Goto self-gravitating string. Due to the
special properties of three-dimensional gravity, the metric is completely
described as a Minkowski space with two identified worldsheets. In the flat
limit, the standard string is recovered. The formalism is developed for an open
string with massive endpoints, but applies to other boundary conditions as
well. We consider another limit, where the string tension vanishes in
geometrical units but the end-masses produce finite deficit angles. In this
limit, our open string reduces to the free-masses solution of Gott, which
possesses closed timelike curves when the relative motion of the two masses is
sufficiently rapid. We discuss the possible causal structures of our spacetimes
in other regimes. It is shown that the induced worldsheet Liouville mode obeys
({\it classically}) a differential equation, similar to the Liouville equation
and reducing to it in the flat limit. A quadratic action formulation of this
system is presented. The possibility and significance of quantizing the
self-gravitating string, is discussed.Comment: 55 page
Cosmological constant influence on cosmic string spacetime
We investigate the line element of spacetime around a linear cosmic string in
the presence of a cosmological constant. We obtain the metric and argue that it
should be discarded because of asymptotic considerations. Then a time dependent
and consistent form of the metric is obtained and its properties are discussed.Comment: 3 page
Transformation of Morphology and Luminosity Classes of the SDSS Galaxies
We present a unified picture on the evolution of galaxy luminosity and
morphology. Galaxy morphology is found to depend critically on the local
environment set up by the nearest neighbor galaxy in addition to luminosity and
the large scale density. When a galaxy is located farther than the virial
radius from its closest neighbor, the probability for the galaxy to have an
early morphological type is an increasing function only of luminosity and the
local density due to the nearest neighbor (). The tide produced by the
nearest neighbor is thought to be responsible for the morphology transformation
toward the early type at these separations. When the separation is less than
the virial radius, i.e. when , its morphology
depends also on the neighbor's morphology and the large-scale background
density over a few Mpc scales () in addition to luminosity and
. The early type probability keeps increasing as increases if
its neighbor is an early type. But the probability decreases as
increases when the neighbor is a late type. The cold gas streaming from the
late type neighbor can be the reason for the morphology transformation toward
late type. The overall early-type fraction increases as increases
when . This can be attributed to the hot halo gas
of the neighbor which is confined by the pressure of the ambient medium held by
the background mass. We have also found that galaxy luminosity depends on
, and that the isolated bright galaxies are more likely to be recent
merger products. We propose a scenario that a series of morphology and
luminosity transformation occur through distant interactions and mergers, which
results in the morphology--luminosity--local density relation.Comment: 14 pages, 7 figures, for higher resolution figures download PDF file
at http://astro.kias.re.kr/docs/trans.pdf ; references added and typos in
section 3.2 corrected; Final version accepted for publication in Ap
(2+1)-Gravity with Moving Particles in an Instantaneous Gauge
By defining a regular gauge which is conformal-like and provides
instantaneous field propagation, we investigate classical solutions of
(2+1)-Gravity coupled to arbitrarily moving point-like particles. We show how
to separate field equations from self-consistent motion and we provide a
solution for the metric and the motion in the two-body case with arbitrary
speed, up to second order in the mass parameters.Comment: 16 pages, LaTeX, no figure
A prescription for probabilities in eternal inflation
Some of the parameters we call ``constants of Nature'' may in fact be
variables related to the local values of some dynamical fields. During
inflation, these variables are randomized by quantum fluctuations. In cases
when the variable in question (call it ) takes values in a continuous
range, all thermalized regions in the universe are statistically equivalent,
and a gauge invariant procedure for calculating the probability distribution
for is known. This is the so-called ``spherical cutoff method''. In
order to find the probability distribution for it suffices to consider a
large spherical patch in a single thermalized region. Here, we generalize this
method to the case when the range of is discontinuous and there are
several different types of thermalized region. We first formulate a set of
requirements that any such generalization should satisfy, and then introduce a
prescription that meets all the requirements. We finally apply this
prescription to calculate the relative probability for different bubble
universes in the open inflation scenario.Comment: 15 pages, 5 figure
Varying c cosmology and Planck value constraints
It has been suggested that by increasing the speed of light during the early
universe various cosmological problems of standard big bang cosmology can be
overcome, without requiring an inflationary phase. However, we find that as the
Planck length and Planck time are then made correspondingly smaller, and
together with the need that the universe should not re-enter a Planck epoch,
the higher models have very limited ability to resolve such problems. For a
constantly decreasing the universe will quickly becomes quantum
gravitationally dominated as time increases: the opposite to standard cosmology
where quantum behaviour is only ascribed to early times.Comment: extended versio
Quantum Stability of (2+1)-Spacetimes with Non-Trivial Topology
Quantum fields are investigated in the (2+1)-open-universes with non-trivial
topologies by the method of images. The universes are locally de Sitter
spacetime and anti-de Sitter spacetime. In the present article we study
spacetimes whose spatial topologies are a torus with a cusp and a sphere with
three cusps as a step toward the more general case. A quantum energy momentum
tensor is obtained by the point stripping method. Though the cusps are no
singularities, the latter cusps cause the divergence of the quantum field. This
suggests that only the latter cusps are quantum mechanically unstable. Of
course at the singularity of the background spacetime the quantum field
diverges. Also the possibility of the divergence of topological effect by a
negative spatial curvature is discussed. Since the volume of the negatively
curved space is larger than that of the flat space, one see so many images of a
single source by the non-trivial topology. It is confirmed that this divergence
does not appear in our models of topologies. The results will be applicable to
the case of three dimensional multi black hole\cite{BR}.Comment: 17 pages, revtex, 3 uuencoded figures containe
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