Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the origin of dark matter axions   We discuss the possible sources of dark matter axions in the early universe.
In the standard thermal scenario, an axion string network forms at the
Peccei-Quinn phase transition $T\sim \fa$ and then radiatively decays into a
cosmological background of axions; to be the dark matter, these axions must
have a mass $\ma \sim 100 \mu eV$ with specified large uncertainties. An
inflationary phase with a reheat temperature below the PQ-scale $T_{reh} \lapp
\fa$ can also produce axion strings through quantum fluctuations, provided that
the Hubble parameter during inflation is large $H_1 \gapp \fa$; this case again
implies a dark matter axion mass $\ma \sim 100 \mu eV$. For a smaller Hubble
parameter during inflation $H_1 \lapp \fa$, `anthropic tuning' allows dark
matter axions to have any mass in a huge range below $\ma\lapp 1 meV$.

24
The categories of this paper are: dg-ga
1
The categories of this paper are: cs
0
The categories of this paper are: hep-ph
37
The categories of this paper are: supr-con
7
The categories of this paper are: hep-th
17
The categories of this paper are: q-fin
34
The categories of this paper are: chem-ph
30
The categories of this paper are: q-alg
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
5
The categories of this paper are: gr-qc
4
The categories of this paper are: cond-mat
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th