Circular polarization of the cosmic microwave background from vector and tensor perturbations. (arXiv:1811.04957v1 [astro-ph.CO])
<a href="http://arxiv.org/find/astro-ph/1/au:+Inomata_K/0/1/0/all/0/1">Keisuke Inomata</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kamionkowski_M/0/1/0/all/0/1">Marc Kamionkowski</a>
Circular polarization of the cosmic microwave background (CMB) can be induced
by Faraday conversion of the primordial linearly polarized radiation as it
propagates through a birefringent medium. Recent work has shown that the
dominant source of birefringence from primordial density perturbations is the
anisotropic background CMB. Here we extend prior work to allow for the
additional birefringence that may arise from primordial vector and tensor
perturbations. We derive the formulas for the power spectrum of the induced
circular polarization and apply those to the standard cosmology. We find the
root-variance of the induced circular polarization to be $sqrt{
3times 10^{-14}$ for scalar perturbations and $sqrt{
10^{-18} (r/0.06)$ for tensor perturbations with a tensor-to-scalar ratio $r$.
Circular polarization of the cosmic microwave background (CMB) can be induced
by Faraday conversion of the primordial linearly polarized radiation as it
propagates through a birefringent medium. Recent work has shown that the
dominant source of birefringence from primordial density perturbations is the
anisotropic background CMB. Here we extend prior work to allow for the
additional birefringence that may arise from primordial vector and tensor
perturbations. We derive the formulas for the power spectrum of the induced
circular polarization and apply those to the standard cosmology. We find the
root-variance of the induced circular polarization to be $sqrt{<V^2>}sim
3times 10^{-14}$ for scalar perturbations and $sqrt{<V^2>}sim 7times
10^{-18} (r/0.06)$ for tensor perturbations with a tensor-to-scalar ratio $r$.
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