Cosmic Microwave Background (CMB) polarization B-modes induced by Faraday Rotation (FR) can provide a distinctive signature of primordial magnetic fields because of their characteristic frequency dependence and because they are only weakly damped on
small scales. FR also leads to mode-coupling correlations between the E and B type polarization, and between the temperature and the B-mode. These additional correlations can further help distinguish magnetic fields from other sources of B-modes. We review the FR induced CMB signatures and present the constraints on primordial magnetism that can be expected from upcoming CMB experiments. Our results suggest that FR of CMB will be a promising probe of primordial magnetic fields.
Cosmic string networks generate cosmological perturbations actively throughout the history of the universe. Thus, the string sourced anisotropy of the cosmic microwave background is not affected by Silk damping as much as the anisotropy seeded by inf
lation. The spectrum of perturbations generated by strings does not match the observed CMB spectrum on large angular scales (l<1000) and is bounded to contribute no more than 10% of the total power on those scales. However, when this bound is marginally saturated, the anisotropy created by cosmic strings on small angular scales l>2000 will dominate over that created by the primary inflationary perturbations. This range of angular scales in the CMB is presently being measured by a number of experiments; their results will test this prediction of cosmic string networks soon.
