696 research outputs found
Gravitational strings. Do we see one?
I present a class of objects called gravitational strings (GS) for their
similarity to the conventional cosmic strings: even though the former are just
singularities in flat spacetime, both varieties are equally "realistic", they
may play equally important cosmological r\^ole and their lensing properties are
akin. I argue that the enigmatic object CSL-1 is an evidence in favor of the
existence of GS.Comment: The published version. Minor correction
Scaling in a SU(2)/Z_3 model of cosmic superstring networks
Motivated by recent developments in superstring theory in the cosmological
context, we examine a field theory which contains string networks with 3-way
junctions. We perform numerical simulations of this model, identify the length
scales of the network that forms, and provide evidence that the length scales
tend towards a scaling regime, growing in proportion to time. We infer that the
presence of junctions does not in itself cause a superstring network to
dominate the energy density of the early Universe.Comment: 12pp, 3 fig
Astrometric Method to Break the Photometric Degeneracy between Binary-source and Planetary Microlensing Perturbations
An extra-solar planet can be detected by microlensing because the planet can
perturb the smooth lensing light curve created by the primary lens. However, it
was shown by Gaudi that a subset of binary-source events can produce light
curves that closely resemble those produced by a significant fraction of
planet/star lens systems, causing serious contamination of a sample of
suspected planetary systems detected via microlensing. In this paper, we show
that if a lensing event is observed astrometrically, one can unambiguously
break the photometric degeneracy between binary-source and planetary lensing
perturbations. This is possible because while the planet-induced perturbation
in the trajectory of the lensed source image centroid shifts points away from
the opening of the unperturbed elliptical trajectory, while the perturbation
induced by the binary source companion points always towards the opening.
Therefore, astrometric microlensing observations by using future high-precision
interferometers will be important for solid confirmation of microlensing planet
detections.Comment: total 5 pages, including 1 figure and no table, ApJ, submitted,
better quality pdf file is avalilable at
http://astroph.chungbuk.ac.kr/~cheongho/publication.htm
The parallax distorsion via a weak microlensing effect
Parallax measurements allow distances to celestial objects to be determined.
Coupled with measurement of their position on the celestial sphere, it gives a
full three-dimensional picture of the location of the objects relative to the
observer. The distortion of the parallax value of a remote source affected by a
weak microlensing is considered. This means that the weak microlensing leads to
distortion of the distance scale. It is shown that the distortions to appear
may change strongly the parallax values in case they amount to several
microseconds of arc. In particular, at this accuracy many measured values of
the parallaxes must be negative.Comment: 34 LaTeX pages, 12 PostScript figure (epsfig.sty
Gravitational-Wave Stochastic Background from Kinks and Cusps on Cosmic Strings
We compute the contribution of kinks on cosmic string loops to stochastic
background of gravitational waves (SBGW).We find that kinks contribute at the
same order as cusps to the SBGW.We discuss the accessibility of the total
background due to kinks as well as cusps to current and planned gravitational
wave detectors, as well as to the big bang nucleosynthesis (BBN), the cosmic
microwave background (CMB), and pulsar timing constraints. As in the case of
cusps, we find that current data from interferometric gravitational wave
detectors, such as LIGO, are sensitive to areas of parameter space of cosmic
string models complementary to those accessible to pulsar, BBN, and CMB bounds.Comment: 24 pages, 3 figure
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