10,839 research outputs found
A Cosmic Microwave Background feature consistent with a cosmic texture
The Cosmic Microwave Background provides our most ancient image of the
Universe and our best tool for studying its early evolution. Theories of high
energy physics predict the formation of various types of topological defects in
the very early universe, including cosmic texture which would generate hot and
cold spots in the Cosmic Microwave Background. We show through a Bayesian
statistical analysis that the most prominent, 5 degree radius cold spot
observed in all-sky images, which is otherwise hard to explain, is compatible
with having being caused by a texture. From this model, we constrain the
fundamental symmetry breaking energy scale to be phi_0 ~ 8.7 x 10^(15) GeV. If
confirmed, this detection of a cosmic defect will probe physics at energies
exceeding any conceivable terrestrial experiment.Comment: Accepted by Science. Published electronically via Science Express on
25 October 2007, http://www.sciencemag.org/cgi/content/abstract/114869
The WMAP cold spot
The WMAP cold spot was found by applying spherical wavelets to the first year
WMAP data. An excess of kurtosis of the wavelet coefficient was observed at
angular scales of around 5 degrees. This excess was shown to be inconsistent
with Gaussian simulations with a p-value of around 1%. A cold spot centered at
(b = -57, l = 209) was shown to be the main cause of this deviation. Several
hypotheses were raised to explain the origin of the cold spot. After performing
a Bayesian template fit a collapsing cosmic texture was found to be the most
probable hypothesis explaining the spot. Here we review the properties of the
cold spot and the possible explanations.Comment: To appear in the "Highlights of Spanish Astrophysics V " Proceedings
of the VIII Scientific Meeting of the Spanish Astronomical Society (SEA) held
in Santander, July 7-11, 200
Determinação da umidade e da temperatura do solo no cultivo de sorgo e feijão na entressafra, em sistema de plantio direto e convencional.
Eficiência de aproveitamento dos nutrientes pelas culturas de sorgo e do feijão na entressafra, em sistema de plantio direto e convencional em sucessão.
Detection of a non-Gaussian Spot in WMAP
An extremely cold and big spot in the WMAP 1-year data is analyzed. Our work
is a continuation of a previous paper (Vielva et al. 2004) where
non-Gaussianity was detected, with a method based on the Spherical Mexican Hat
Wavelet (SMHW) technique. We study the spots at different thresholds on the
SMHW coefficient maps, considering six estimators, namely number of maxima,
number of minima, number of hot and cold spots, and number of pixels of the
spots. At SMHW scales around 4 degrees (10 degrees on the sky), the data
deviate from Gaussianity. The analysis is performed on all sky, the northern
and southern hemispheres, and on four regions covering all the sky. A cold spot
at (b = -57, l = 209) is found to be the source of this non-Gaussian signature.
We compare the spots of our data with 10000 Gaussian simulations, and conclude
that only around 0.2% of them present such a cold spot. Excluding this spot,
the remaining map is compatible with Gaussianity and even the excess of
kurtosis in Vielva et al. 2004, is found to be due exclusively to this spot.
Finally, we study whether the spot causing the observed deviation from
Gaussianity could be generated by systematics or foregrounds. None of them seem
to be responsible for the non-Gaussian detection.Comment: 14 pages, references and two new sections (4.4, 5.3) added, accepted
for publication in MNRA
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