Standard Model Prediction for Cosmological 21cm Circular Polarization

Abstract

Before cosmic reionization, hydrogen atoms acquire a spin polarization quadrupole through interaction with the anisotropic 21-cm radiation field. The interaction of this quadrupole with anisotropies in the cosmic microwave background (CMB) radiation field gives a net spin orientation to the hydrogen atoms. The 21-cm radiation emitted by these spin-oriented hydrogen atoms is circularly polarized. Here, we reformulate succinctly the derivation of the expression for this circular polarization in terms of Cartesian (rather than spherical) tensors. We then compute the angular power spectrum of the observed Stokes-$V$ parameter in the standard $\Lambda$CDM cosmological model and show how it depends on redshift, or equivalently, the observed frequency.

5 pages, 2 figures; added references

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Cited by in corpus (2)

• Linear Polarization of the 21 cm Line from the Epoch of Reionization
• Cross-correlation of the Polarizations of the 21-cm and Cosmic Microwave Backgrounds