Journal
JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS
Volume -, Issue 5, Pages -Publisher
IOP Publishing Ltd
DOI: 10.1088/1475-7516/2022/05/016
Keywords
CMBR polarisation; CMBR theory; reionization
Funding
- JSPS KAKENHI [19K03851]
- Grants-in-Aid for Scientific Research [19K03851] Funding Source: KAKEN
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This article investigates the dependence of the ratio of cosmic microwave background (CMB) polarization power spectra on the process of reionization. The results indicate that the ratio is not very sensitive to the reionization process at low redshifts but sensitive to the value of optical depth. However, at l = 2, the ratio is almost unaffected by the reionization process and is approximately half of the value of the tensor-to-scalar ratio.
We investigate how much the ratio of cosmic microwave background (CMB) polarization power spectra C-l(BB)/C-l(EE) at low-l (l less than or similar to 10) depends on the process of reionization. Both such low-l B-mode and E-mode polarization powers are dominantly produced by Thomson scattering of CMB photons off the free electrons which are produced in the process of reionization. Since the reionization should be finished until at least the redshift z similar or equal to 6 and the low-l polarization powers are produced at late time, the ratio is rather insensitive by the ionization process at higher redshifts, but it is sensitive to the value of optical depth. The value of the ratio at l = 2, however, is almost insensitive to the reionization process including the value of optical depth, and the value is approximately half of the value of tensor-to-scalar ratio. This fact can be utilized for future determination of tensor-to-scalar ratio in spite of the ambiguity due to cosmic variance.
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