Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Semi-numeric simulations of helium reionization and the fluctuating
  radiation background   Recent He II Lyman-alpha forest observations from 2.0 < z < 3.2 show large
fluctuations in the optical depth at z > 2.7. These results point to a
fluctuating He-ionizing background, which may be due to the end of helium
reionization of this era. We present a fast, semi-numeric procedure to
approximate detailed cosmological simulations. We compute the distribution of
dark matter halos, ionization state of helium, and density field at z = 3 in
broad agreement with recent simulations. Given our speed and flexibility, we
investigate a range of ionizing source and active quasar prescriptions.
Spanning a large area of parameter space, we find order-of-magnitude
fluctuations in the He II ionization rate in the post-reionization regime.
During reionization, the fluctuations are even stronger and develop a bimodal
distribution, in contrast to semi-analytic models and the hydrogen equivalent.
These distributions indicate a low-level ionizing background even at
significant He II fractions.

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The categories of this paper are: adap-org
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The categories of this paper are: q-alg
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The categories of this paper are: cond-mat
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The categories of this paper are: dg-ga
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The categories of this paper are: alg-geom
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: cmp-lg
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex