Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Axions and their Relatives   A review of the status of axions and axion-like particles is given. Special
attention is devoted to the recent results of the PVLAS collaboration, which
are in conflict with the CAST data and with the astrophysical constraints.
Solutions to the puzzle and the implications for new physics are discussed. The
question of axion-like particles being dark matter is also addressed.

13
The categories of this paper are: quant-ph
14
The categories of this paper are: math-ph
23
The categories of this paper are: solv-int
20
The categories of this paper are: acc-phys
16
The categories of this paper are: stat
24
The categories of this paper are: dg-ga
32
The categories of this paper are: atom-ph
36
The categories of this paper are: cmp-lg
26
The categories of this paper are: bayes-an
37
The categories of this paper are: supr-con
4
The categories of this paper are: cond-mat
15
The categories of this paper are: nucl-ex
1
The categories of this paper are: cs
2
The categories of this paper are: math
33
The categories of this paper are: plasm-ph
9
The categories of this paper are: nlin