Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Was the Universe neutral beyond redshift six?   We provide measurements of the neutral hydrogen fraction xHI at z~6, by
comparing semi-analytical models of the Lyalpha forest with observations of
high-z quasars and Gamma Ray Bursts absorption spectra. We analyze the
transmitted flux in a sample of 17 QSOs spectra at 5.74<zem<6.42 studying
separately the narrow transmission windows (peaks) and the wide dark portions
(gaps) in the observed absorption spectra. By comparing the statistics of these
spectral features with our models, we conclude that xHI evolves smoothly from
10^{-4.4} at z=5.3 to 10^{-4.2} at z=5.6, with a robust upper limit xHI<0.36 at
z=6.3. We show the results of the first-ever detected transverse proximity
effect in the HI Lyalpha forest, produced by the HII region of the faint quasar
RD J1148+5253 at z=5.70 intervening along the LOS of SDSS J1148+5251 at z=6.42.
Moreover, we propose a novel method to study cosmic reionization using
absorption line spectra of high-redshift GRBs afterglows. We show that the time
evolution and the statistics of gaps in the observed spectra represent
exquisite tools to discriminate among different reionization models. By
applying our methods to GRB 050904 detected at z=6.29, we show that the
observation of this burst provides strong indications of a highly ionized
intergalactic medium at z~6, with an estimated mean neutral hydrogen fraction
xHI=6.4\pm 0.3\times 10^{-5} along that line of sight.

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The categories of this paper are: dg-ga
1
The categories of this paper are: cs
14
The categories of this paper are: math-ph
12
The categories of this paper are: nucl-th
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The categories of this paper are: acc-phys
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The categories of this paper are: chem-ph
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The categories of this paper are: econ
3
The categories of this paper are: physics
25
The categories of this paper are: patt-sol
26
The categories of this paper are: bayes-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: q-alg
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The categories of this paper are: hep-th
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The categories of this paper are: solv-int