Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Reionization History at High Redshifts II: Estimating the Optical
  Depth to Thomson Scattering from CMB Polarization   In light of the recent inference of a high optical depth to Thomson
scattering, tau, from the WMAP data we investigate the effects of extended
periods of partial ionization and ask if the value of tau inferred by assuming
a single sharp transition is an unbiased estimate. We construct and consider
several representative ionization models and evaluate their signatures in the
CMB. If tau is estimated with a single sharp transition we show that there can
be a significant bias in the derived value (and therefore a bias in sigma8 as
well). For WMAP noise levels the bias in tau is smaller than the statistical
uncertainty, but for Planck or a cosmic variance limited experiment the tau
bias could be much larger than the statistical uncertainties. This bias can be
reduced in the ionization models we consider by fitting a slightly more
complicated ionization history, such as a two-step ionization process. Assuming
this two-step process we find the Planck satellite can simultaneously determine
the initial redshift of reionization to +-2 and tau to +-0.01 Uncertainty about
the ionization history appears to provide a limit of about 0.005 on how well
tau can be estimated from CMB polarization data, much better than expected from
WMAP but significantly worse than expected from cosmic-variance limits.

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The categories of this paper are: cond-mat
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: nlin
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The categories of this paper are: gr-qc
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The categories of this paper are: bayes-an
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The categories of this paper are: atom-ph
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The categories of this paper are: physics
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The categories of this paper are: nucl-th
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The categories of this paper are: plasm-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: adap-org
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio