27 research outputs found
Hyperbolic Universes with a Horned Topology and the CMB Anisotropy
We analyse the anisotropy of the cosmic microwave background (CMB) in
hyperbolic universes possessing a non-trivial topology with a fundamental cell
having an infinitely long horn. The aim of this paper is twofold. On the one
hand, we show that the horned topology does not lead to a flat spot in the CMB
sky maps in the direction of the horn as stated in the literature. On the other
hand, we demonstrate that a horned topology having a finite volume could
explain the suppression of the lower multipoles in the CMB anisotropy as
observed by COBE and WMAP
Ellipticity of Structures in CMB Sky Maps
We study the ellipticity of contour lines in the sky maps of the cosmic
microwave background (CMB) as well as other measures of elongation. The
sensitivity of the elongation on the resolution of the CMB maps which depends
on the pixelization and the beam profile of the detector, is investigated. It
is shown that the current experimental accuracy does not allow to discriminate
between cosmological models which differ in curvature by Delta Omega_tot=0.05.
Analytical expressions are given for the case that the statistical properties
of the CMB are those of two-dimensional Gaussian random fields
CMB Anisotropy of Spherical Spaces
The first-year WMAP data taken at their face value hint that the Universe
might be slightly positively curved and therefore necessarily finite, since all
spherical (Clifford-Klein) space forms M^3 = S^3/Gamma, given by the quotient
of S^3 by a group Gamma of covering transformations, possess this property. We
examine the anisotropy of the cosmic microwave background (CMB) for all typical
groups Gamma corresponding to homogeneous universes. The CMB angular power
spectrum and the temperature correlation function are computed for the
homogeneous spaces as a function of the total energy density parameter
Omega_tot in the large range [1.01, 1.20] and are compared with the WMAP data.
We find that out of the infinitely many homogeneous spaces only the three
corresponding to the binary dihedral group T*, the binary octahedral group O*,
and the binary icosahedral group I* are in agreement with the WMAP
observations. Furthermore, if Omega_tot is restricted to the interval [1.00,
1.04], the space described by T* is excluded since it requires a value of
Omega_tot which is probably too large being in the range [1.06, 1.07]. We thus
conclude that there remain only the two homogeneous spherical spaces S^3/O* and
S^3/I* with Omega_tot of about 1.038 and 1.018, respectively, as possible
topologies for our Universe.Comment: A version with high resolution sky maps can be obtained at
http://www.physik.uni-ulm.de/theo/qc
CMB Anisotropy of the Poincare Dodecahedron
We analyse the anisotropy of the cosmic microwave background (CMB) for the
Poincare dodecahedron which is an example for a multi-connected spherical
universe. We compare the temperature correlation function and the angular power
spectrum for the Poincare dodecahedral universe with the first-year WMAP data
and find that this multi-connected universe can explain the surprisingly low
CMB anisotropy on large scales found by WMAP provided that the total energy
density parameter Omega_tot is in the range 1.016...1.020. The ensemble average
over the primordial perturbations is assumed to be the scale-invariant
Harrison-Zel'dovich spectrum. The circles-in-the-sky signature is studied and
it is found that the signal of the six pairs of matched circles could be missed
by current analyses of CMB sky maps
CMB Alignment in Multi-Connected Universes
The low multipoles of the cosmic microwave background (CMB) anisotropy
possess some strange properties like the alignment of the quadrupole and the
octopole, and the extreme planarity or the extreme sphericity of some
multipoles, respectively. In this paper the CMB anisotropy of several
multi-connected space forms is investigated with respect to the maximal angular
momentum dispersion and the Maxwellian multipole vectors in order to settle the
question whether such spaces can explain the low multipole anomalies in the
CMB