Daniel Grin, Olivier Doré, Marc Kamionkowski
Baryon-density perturbations of large amplitude may exist if they are
compensated by dark-matter perturbations so that the total density remains
unchanged. Big-bang nucleosynthesis and galaxy clusters allow the amplitudes of
these compensated isocurvature perturbations (CIPs) to be as large as
$\sim10%$. CIPs will modulate the power spectrum of cosmic microwave background
(CMB) fluctuations---those due to the usual adiabatic perturbations---as a
function of position on the sky. This leads to correlations between different
spherical-harmonic coefficients of the temperature/polarization map, and it
induces B modes in the CMB polarization. Here, the magnitude of these effects
is calculated and techniques to measure them are introduced. While a CIP of
this amplitude can be probed on the largest scales with WMAP, forthcoming CMB
experiments should improve the sensitivity to CIPs by at least an order of
magnitude.
View original:
http://arxiv.org/abs/1107.1716
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