Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Observation of the new emission line at ~3.5 keV in X-ray spectra of
  galaxies and galaxy clusters   The detection of an unidentified emission line in X-ray spectra of cosmic
objects would be a 'smoking gun' signature for particle physics beyond the
Standard Model. More than a decade of its extensive searches results in several
narrow faint emission lines reported at 3.5, 8.7, 9.4 and 10.1 keV. The most
promising of them is the emission line at ~3.5 keV reported in spectra of
several nearby galaxies and galaxy clusters. Here I summarize its up-to-date
status, overview its possible interpretations, including an intriguing
connection with radiatively decaying dark matter, and outline future directions
for its studies.

32
The categories of this paper are: atom-ph
37
The categories of this paper are: supr-con
21
The categories of this paper are: adap-org
11
The categories of this paper are: hep-lat
25
The categories of this paper are: patt-sol
12
The categories of this paper are: nucl-th
23
The categories of this paper are: solv-int
31
The categories of this paper are: ao-sci
2
The categories of this paper are: math
16
The categories of this paper are: stat
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
22
The categories of this paper are: chao-dyn
13
The categories of this paper are: quant-ph
15
The categories of this paper are: nucl-ex
17
The categories of this paper are: q-fin