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The Structure of Cosmological Polarization Since the polarization of the CMB arose from gradients in the velocity field of the primordial plasma, the structure of this cosmological polarization depends upon the dynamics of the early universe. The detailed measurements of these polarization anisotropies will therefore provide important cosmological information. Furthermore, fairly robust predictions regarding the size of the polarized signal can be made using the currently available data on the temperature anisotropies of the CMB. These temperature fluctuations reflect variations in the density of the plasma, not velocity fields (but see Hu and Sugiyama, 1995), so the temperature anisotropies do not directly determine the size of the cosmological polarization. Instead, the correlation between the temperature and polarization anistropies is due to the dynamics of the primordial plasma itself, which coupled the density variations to the bulk flows. The accurate modeling of these dynamics typically requires computer programs like CMBFAST to solve the appropriate general relativistic Boltzmann equations. However, the fundamental features of these CMB anisotropies can be understood intuitively, as shown below.
Figure 1.6: CMB power spectra, showing the size of the temperature and polarization anisotropies as a function of angular scale. Conventionally, the angular scale is parametrized by the multipole moment from the spherical harmonic decomposition . The ordinate axis gives the amplitude of the variations per logarithmic interval in (which technically makes this a plot of the spectral density, or the square root of the power spectrum). The curves are the power spectra predicted by various cosmological models obtained from CMBFAST, for both the temperature anisotropies and the polarization anisotropies. The polarization power spectra are the three curves peaking in the lower right corner of the plot. Note that alterations in the assumed cosmological model produce concordant changes in the temperature and polarization power spectra. The shaded boxes represent the results of measurements of the actual temperature anisotropies. A fixed number of dots per box has been used to give more visual weight to experiments with smaller error bars. The Origin of Cosmological Polarization The Structure of Cosmological Polarization Power Spectra and the Structure of CMB Anisotropies Initial Conditions and Inflation The Evolution of Perturbations and Acoustic Oscillations Acoustic Oscillations and Apparent Temperature Variations |
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