A CMB Polarization Primer
Wayne Hu &
We present a pedagogical and phenomenological introduction to the study
of cosmic microwave background (CMB) polarization to build intuition
about the prospects and challenges facing its detection.
Thomson scattering of temperature anisotropies on the last
scattering surface generates a linear polarization pattern on the sky that
can be simply read off from their quadrupole moments. These in turn
correspond directly to the fundamental scalar (compressional), vector
(vortical), and tensor (gravitational wave) modes of cosmological
perturbations. We explain the origin and phenomenology of the geometric
distinction between these patterns in terms of the so-called electric and
magnetic parity modes, as well as their correlation with the temperature
pattern. By its isolation of the last scattering surface and the
various perturbation modes, the polarization provides unique
information for the phenomenological reconstruction of the cosmological model.
Finally we comment on the comparison of theory with experimental data
and prospects for the future detection of CMB polarization.