Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Cosmic rays and the primordial gas   One of the most outstanding problems in the gravitational collapse scenario
of early structure formation is the cooling of primordial gas to allow for
small mass objects to form. As the neutral primordial gas is a poor radiator at
temperatures (T\le10^4\unit{K}), molecular hydrogen is needed for further
cooling down to temperatures (T\sim100\unit{K}). The formation of molecular
hydrogen is catalyzed by the presence of free electrons, which could be
provided by the ionization due to an early population of cosmic rays. In order
to investigate this possibility we developed a code to study the effects of
ionizing cosmic rays on the thermal and chemical evolution of primordial gas.
We found that cosmic rays can provide enough free electrons needed for the
formation of molecular hydrogen, and therefore can increase the cooling ability
of such primordial gas under following conditions: A dissociating photon flux
with (F<10^{-18}\unit{erg cm^{-2} Hz^{-1} s^{-1}}), initial temperature of the
gas (\sim10^{3}\unit{K}), total gas number densities (n\ge1\unit{cm^{-3}}),
Cosmic ray sources with (\dot{\epsilon}_{CR}>10^{-33}\unit{erg cm^{-3}
s^{-1}}).

18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
30
The categories of this paper are: q-alg
35
The categories of this paper are: mtrl-th
23
The categories of this paper are: solv-int
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
0
The categories of this paper are: hep-ph
25
The categories of this paper are: patt-sol
17
The categories of this paper are: q-fin
28
The categories of this paper are: alg-geom
14
The categories of this paper are: math-ph
11
The categories of this paper are: hep-lat