Isotropy of the early universe from CMB anisotropies

Abstract

The acoustic peak in the CMB power spectrum is sensitive to causal processes and cosmological parameters in the early universe up to the time of last scattering. We provide limits on correlated spatial variations of the peak height and peak position and interpret these as constraints on the spatial variation of the cosmological parameters (baryon density, cold dark matter density and cosmological constant as well as the amplitude and tilt of the original fluctuations). We utilize recent work of Hansen, Banday and Górski (HBG) who have studied the spatial isotropy of the power spectrum as measured by WMAP by performing the power spectrum analysis on smaller patches of the sky. We find that there is no statistically significant correlated asymmetry of the peak. HBG have also provided preliminary indications of a preferred direction in the lower angular momentum range( ℓ ∼ 2-40) and we show how possible explanations of this asymmetry are severely constrained by the data on the acoustic peak. Finally we show a possible non-gaussian feature in the data, associated with a difference in the northern and southern galactic hemispheres.

Relating the inhomogeneous power spectrum to the CMB hemispherical anisotropy

“…Simulations at higher l also require much higher computation time. Finally, as we have discussed above, the signal of dipole modulation is expected to die down for values of l beyond a few hundred [14][15][16][17]. We hope to extend our analysis to higher values of l in a future publication.…”

“…Hence the results obtained by WMAP and PLANCK observations are consistent with one another. There were indications that the hemispherical anisotropy might extend to multipoles higher than 64 [4,5], however, the effect is found to be absent beyond l ∼ 500 [14,15]. The large scale structure surveys also do not show any evidence for this anisotropy [16,17].…”

A hemispherical power asymmetry from inflation

“…However, if the inflaton and curvaton decays products differ, then there may be an isocurvature component [21,27]. Finally, the simplest scenario predicts a scale-invariant power asymmetry; the asymmetry has been found at multipole moments ℓ < ∼ 40, but there are claims that it does not extend to higher ℓ [28]. If this result holds, it will be interesting to see whether the departure from scale invariance can be obtained by suitably altering the power spectra for the curvaton and inflaton.…”

Constraints on cosmic hemispherical power anomalies from quasars

“…(4) Only limited information is available about the ℓ-dependence of the asymmetry. There are indications that it continues at least to ℓ = 80 [12] and perhaps beyond [11], but other analyses have found no evidence for an amplitude asymmetry at the first acoustic peak [28].…”