Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Sterile dark matter and reionization   Sterile neutrinos with masses in the keV range can be the dark matter, and
their emission from a supernova can explain the observed velocities of pulsars.
The sterile neutrino decays could produce the x-ray radiation in the early
universe, which could have an important effect on the formation of the first
stars. X-rays could ionize gas and could catalyze the production of molecular
hydrogen during the ``dark ages''. The increased fraction of molecular hydrogen
could facilitate the cooling and collapse of the primordial gas clouds in which
the first stars were formed.

27
The categories of this paper are: comp-gas
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
3
The categories of this paper are: physics
22
The categories of this paper are: chao-dyn
4
The categories of this paper are: cond-mat
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
5
The categories of this paper are: gr-qc
18
The categories of this paper are: econ
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
16
The categories of this paper are: stat