448 research outputs found
Missing Power vs low-l Alignments in the Cosmic Microwave Background: No Correlation in the Standard Cosmological Model
On large angular scales (greater than about 60 degrees), the two-point
angular correlation function of the temperature of the cosmic microwave
background (CMB), as measured (outside of the plane of the Galaxy) by the
Wilkinson Microwave Anisotropy Probe, shows significantly lower large-angle
correlations than expected from the standard inflationary cosmological model.
Furthermore, when derived from the full CMB sky, the two lowest cosmologically
interesting multipoles, the quadrupole (l=2) and the octopole (l=3), are
unexpectedly aligned with each other. Using randomly generated full-sky and
cut-sky maps, we investigate whether these anomalies are correlated at a
statistically significant level. We conclusively demonstrate that, assuming
Gaussian random and statistically isotropic CMB anisotropies, there is no
statistically significant correlation between the missing power on large
angular scales in the CMB and the alignment of the l=2 and l=3 multipoles. The
chance to measure the sky with both such a lack of large-angle correlation and
such an alignment of the low multipoles is thus quantified to be below 10^{-6}.Comment: 4 Pages, 1 Figur
Shape of Cosmic String Loops
Complicated cosmic string loops will fragment until they reach simple,
non-intersecting ("stable") configurations. Through extensive numerical study
we characterize these attractor loop shapes including their length, velocity,
kink, and cusp distributions. We find that an initial loop containing M
harmonic modes will, on average, split into 3M stable loops. These stable loops
are approximately described by the degenerate kinky loop, which is planar and
rectangular, independently of the number of modes on the initial loop. This is
confirmed by an analytic construction of a stable family of perturbed
degenerate kinky loops. The average stable loop is also found to have a 40%
chance of containing a cusp. We examine the properties of stable loops of
different lengths and find only slight variation. Finally we develop a new
analytic scheme to explicitly solve the string constraint equations.Comment: 11 pages, 19 figures. See http://www.phys.cwru.edu/projects/strings/
for more information, movies, code, etc. Minor clarification suggested by
referee. Accepted for publication in Phys. Rev.
Large Scale Baryon Isocurvature Inhomogeneities
Big bang nucleosynthesis constraints on baryon isocurvature perturbations are
determined. A simple model ignoring the effects of the scale of the
perturbations is first reviewed. This model is then extended to test the claim
that large amplitude perturbations will collapse, forming compact objects and
preventing their baryons from contributing to the observed baryon density. It
is found that baryon isocurvature perturbations are constrained to provide only
a slight increase in the density of baryons in the universe over the standard
homogeneous model. In particular it is found that models which rely on power
laws and the random phase approximation for the power spectrum are incompatible
with big bang nucleosynthesis unless an {\em ad hoc}, small scale cutoff is
included.Comment: 11pages + 8figures, LaTeX (2.09), postscript figures available via
anonymous ftp from oddjob.uchicago.edu:/ftp/ibbn/fig?.ps where ?=1-8 or via
email from [email protected], Fermilab-Pub-94/???-A and UMN-TH-1307/9
Large-angle anomalies in the CMB
We review the recently found large-scale anomalies in the maps of temperature
anisotropies in the cosmic microwave background. These include alignments of
the largest modes of CMB anisotropy with each other and with geometry and
direction of motion of the Solar System, and the unusually low power at these
largest scales. We discuss these findings in relation to expectation from
standard inflationary cosmology, their statistical significance, the tools to
study them, and the various attempts to explain them.Comment: Review in the Advances in Astronomy special issue "Testing the
Gaussianity and Statistical Isotropy of the Universe" (eds. D. Huterer, E.
Komatsu and S. Shandera); 16 pages, 7 figures. v2 matches the published
versio
Is the low-l microwave background cosmic?
The large-angle (low-l) correlations of the Cosmic Microwave Background
exhibit several statistically significant anomalies compared to the standard
inflationary big-bang model, however no connection has hitherto been drawn
between them. Here we show that the quadrupole and octopole are far more
correlated (99.97% C.L.) than previously thought. The quadrupole plane and the
three octopole planes are remarkably aligned. Three of these planes are
orthogonal to the ecliptic at a level inconsistent with gaussian random
statistically isotropic skies at 99.8% C.L., and the normals to these planes
are aligned at 99.9% C.L. with the direction of the cosmological dipole and
with the equinoxes. The remaining octopole plane is orthogonal to the
supergalactic plane at >99.9% C.L. In a combined quadrupole-octopole map, the
ecliptic plane narrowly threads between a hot spot and a cold spot over
approximately 1/3 of the sky, and separates the three strongest extrema (in the
south ecliptic hemisphere) from the three weakest extrema (in the north
ecliptic hemisphere).Comment: 4 pages, 3 figures; more figures available at:
http://www.phys.cwru.edu/projects/mpvectors/ PRL in press versio
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