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Post Info TOPIC: WMAP Cold Spot
Blobrana


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WMAP Cold Spot
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Title: Disks in the sky: A reassessment of the WMAP "cold spot"
Authors: Ray Zhang, Dragan Huterer (University of Michigan)

We reassess the evidence that WMAP temperature maps contain a statistically significant "cold spot" by repeating the analysis using simple circular top-hat (disk) weights, as well as Gaussian weights of varying width. Contrary to previous results that used Spherical Mexican Hat Wavelets, we find no significant signal at any scale when we compare the coldest spot from our sky to ones from simulated Gaussian random, isotropic maps. We trace this apparent discrepancy to the fact that WMAP cold spot's temperature profile just happens to favour the particular profile given by the wavelet. Since randomly generated maps typically do not exhibit this coincidence, we conclude that the original cold spot significance originated at least partly due to a fortuitous choice of using a particular basis of weight functions. We also examine significance of a more general measure that returns the most significant result among several choices of the weighting function, angular scale of the spot, and the statistics applied, and again find a null result.

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Blobrana


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The Cold Spot
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Title: The Cold Spot as a Large Void: Lensing Effect on CMB Two and Three Point Correlation Functions
Authors: Isabella Masina, Alessio Notari

The "Cold Spot" in the CMB sky could be due to the presence of an anomalous huge spherical underdense region - a "Void" - of a few hundreds Mpc/h radius. Such a structure would have an impact on the CMB two-point (power spectrum) and three-point (bispectrum) correlation functions not only at low-l, but also at high-l through Lensing, which is a unique signature of a Void. Modelling such an underdensity with an LTB metric, we show that for the power spectrum the effect should be visible already in the WMAP data if the Void radius is at least 400 Mpc/h, while it will be visible by the Planck satellite for any Void radius. We also speculate that this could be linked to the high-l detection of an hemispherical power asymmetry in the sky. Moreover, there should be non-zero correlations in the non-diagonal two-point function. For the bispectrum, the effect becomes important for squeezed triangles with two very high-l's: this signal can be detected by Planck if the Void radius is at least 600 Mpc/h. We have also estimated the contamination of the primordial non-Gaussianity f_NL due to this signal, which turns out to be negligible.

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Blobrana


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RE: WMAP Cold Spot
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How to lose a hole the size of a universe

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The void, which supposedly contained far fewer stars and galaxies than expected, could be nothing but a statistical artefact.
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Blobrana


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A giant hole in the cosmos that shocked astrophysicists last year may not exist after all. A re-examination of the area has found that the 'void', which supposedly contained far fewer stars and galaxies than expected, could be a statistical artefact.
The apparent void was spotted by Lawrence Rudnick and colleagues at the University of Minnesota in Minneapolis. Rudnick had become intrigued by another puzzling finding: a cold spot in the cosmic microwave background measured by the WMAP spacecraft. He used data from the Very Large Array telescope at the National Radio Astronomy Observatory near Socorro, New Mexico, to study the area and concluded that the cold spot coincided with a void almost 1 billion light years across, the largest anyone had ever seen.

Source New Scientist
(Embargoed until 18:00 BST today)

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Blobrana


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Title: The CMB cold spot: texture, cluster or void?
Authors: M. Cruz, E. Martinez-Gonzalez, P. Vielva, J.M. Diego, M. Hobson, N. Turok

The non-Gaussian cold spot found in the WMAP data has created controversy about its origin. Here we calculate the Bayesian posterior probability ratios for three different models that could explain the cold spot. A recent work claimed that the Spot could be caused by a cosmic texture, while other papers suggest that it could be due to the gravitational effect produced by an anomalously large void. Also the Sunyaev-Zeldovich effect caused by a cluster is taken into account as a possible origin. We perform a template fitting on a 20 degrees radius patch centred at Galactic coordinates (b = -57circ, l = 209) and calculate the posterior probability ratios for the void and Sunyaev-Zeldovich models, comparing the results to those obtained with textures. Taking realistic priors for the parameters, the texture interpretation is favoured, while the void and Sunyaev-Zeldovich hypotheses are discarded. The temperature decrement produced by voids or clusters is negligible considering realistic values for the parameters.

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Blobrana


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Relic topological defects
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Title: Relic topological defects from brane annihilation simulated in superfluid 3He
Authors: D. I. Bradley, S. N. Fisher, A. M. Guénault, R. P. Haley, J. Kopu, H. Martin, G. R. Pickett, J. E. Roberts & V. Tsepelin

Although it is widely accepted that to resolve the 'horizon' problem the early Universe must have undergone a sudden expansion (cosmic inflation), what mechanism drove this process is less clear. In the braneworld scenario, it is suggested that inflationary epochs may have been initiated and terminated by brane collisions and annihilations. Branes are objects of lower dimensionality embedded in a higher-dimensional matrix. For example, we may live on a three-dimensional brane embedded in a four-dimensional matrix. However, such structures are so far removed from everyday reality that bringing physical insight to bear is difficult. Here we report laboratory experiments where we simulate brane annihilation using the closest brane analogue to which we have access, the coherent phase boundary between the two phases of superfluid 3He. When two branes collide or annihilate, topological defects may be created, whose influence may still be detectable today. By creating a braneantibrane pair in superfluid 3He and subsequently annihilating it, we can detect that defects are indeed created in the superfluid texture (the superfluid analogue of spacetime), thus confirming that the concept of defect formation after brane annihilation in the early Universe can be reproduced in analogous systems in the laboratory.

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Blobrana


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Posts: 131433
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RE: WMAP Cold Spot
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Title: The mystery of the WMAP cold spot
Authors: Pavel D. Naselsky (1), Per Rex Christensen (1), Peter Coles (2), Oleg Verkhodanov (3), Dmitry Novikov (4,5), Jaiseung Kim (1) ((1) Niels Bohr Institute, Copenhagen, Denmark; (2) School of Physics and Astronomy, Cardiff University, Wales, United Kingdom; (3) Special astrophysical observatory, Nizhnij Arkhyz, Russia; (4) Imperial College, London, United Kingdom; (5) AstroSpace Center of Lebedev Physical Institute, Moscow, Russia)

The first and third year data releases from the WMAP provide evidence of an anomalous Cold Spot (CS) at galactic latitude b=-57deg and longitude l=209deg. We have examined the properties of the CS in some detail in order to assess its cosmological significance. We have performed a cluster analysis of the local extrema in the CMB signal to show that the CS is actually associated with a large group of extrema rather than just one. In the light of this we have re-examined the properties of the WMAP ILC and co-added "cleaned" WCM maps, which have previously been used for the analysis of the properties of the signal in the vicinity of the CS. These two maps have remarkably similar properties on equal latitude rings for |b|>30deg, as well as in the vicinity of the CS. We have also checked the idea that the CMB signal has a non-Gaussian tail, localized in the low multipole components of the signal. For each ring we apply a linear filter with characteristic scale R, dividing the CMB signal in two parts: the filtered part, with characteristic scale above that of the filter R, and the difference between the initial and filtered signal. Using the filter scale as a variable, we can maximise the skewness and kurtosis of the smoothed signal and minimise these statistics for the difference between initial and filtered signal. We have discovered that the shape of the CS is formed primarily by the components of the CMB signal represented by multipoles between 10<=L<=20, with a corresponding angular scale about 5-10 degs. This signal leads to modulation of the whole CMB sky, clearly seen at |b|>30deg in both the ILC and WCM maps, rather than a single localized feature. After subtraction of this modulation, the remaining part of the CMB signal appears to be consistent with statistical homogeneity and Gaussianity.

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Blobrana


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Earlier this year astronomers from the University of Minnesota discovered a massive void of space that measured nearly a billion light years across. It was an intriguing discovery, in a universe that is filled with seemingly infinite objects.
The team was working with sensor data retrieved by the NASAs WMAP (Wilkinson Microwave Anisotropy Probe) satellite.
What was even more fascinating was the fact that a hole this size was essentially impossible to explain under the constraints of current scientific theory.
Enter University of North Carolina at Chapel Hill physics Professor Laura Mersini-Houghton.
she describes the hole as the unmistakable imprint of another universe beyond the edge of our own.
theory posits that there are in fact two giant hole


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Blobrana


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Astronomers announced in August 2007 the discovery of a large hole at the edge of our universe. Since then, theoretical physicist and cosmologist Laura Mersini-Houghton and colleagues have claimed it is an unmistakable imprint of another universe beyond the edge of our own.
The article entitled Astronomers Find Enormous Hole in the Universe discusses the August 2007 discovery of the hole. It is located at the National Radio Astronomy Observatory website.
Dr. Laura Mersini-Houghton is a theoretical physicist and cosmologist at the University of North Carolina (Chapel Hill).
The hole is estimated to be almost one billion light-years across, where one light-year is about 9.5 trillion kilometres  and is located within the constellation Eridanus.
The Mersini-Houghton team states that the hole is another universe at the edge of our own universe. Such an explanation, if true, would be the first experimental evidence of such an exo-universe, or a universe outside of our own universe.

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Blobrana


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In August , radio astronomers announced that they had found an enormous hole in the universe. Nearly a billion light years across, the void lies in the constellation Eridanus and has far fewer stars, gas and galaxies than usual. It is bigger than anyone imagined possible and is beyond the present understanding of cosmology. What could cause such a gaping hole? One team of physicists has a breathtaking explanation:

"It is the unmistakable imprint of another universe beyond the edge of our own" - Laura Mersini-Houghton of the University of North Carolina at Chapel Hill.

It is a staggering claim. If Mersini-Houghton's team is right, the giant void is the first experimental evidence for another universe. It would also vindicate string theory, our most promising understanding of how the universe works at its most fundamental level.

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