Kavli Affiliate: Toshiya Namikawa
| First 5 Authors: Hanchun Jiang, Toshiya Namikawa, , ,
| Summary:
We explore the impact of the reionization history on examining the shape of
the power spectrum of the primordial gravitational waves (PGWs) with the cosmic
microwave background (CMB) polarization. The large-scale CMB generated from the
reionization epoch is important in probing the PGWs from all-sky experiments,
such as LiteBIRD. The reionization model has been constrained by several
astrophysical observations. However, its uncertainty could impact constraining
models of the PGWs if we use large-scale CMB polarization. Here, by expanding
the analysis of Mortonson & Hu (2007), we estimate how reionization uncertainty
impacts constraints on a generic primordial tensor power spectrum. We assume
that CMB polarization is measured by a LiteBIRD-like experiment and the tanh
model is adopted for a theoretical template when we fit data. We show that
constraints are almost unchanged even if the true reionization history is
described by an exponential model, where all parameters are within 68%
Confidence Level (CL). We also show an example of the reionization history that
the constraints on the PGWs are biased more than 68% CL. Even in that case,
using E-mode power spectrum on large scales would exclude such a scenario and
make the PGW constraints robust against the reionization uncertainties.
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