Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On dark atoms, massive dark photons and millicharged sub-components   We present a simple model of two dark matter species with opposite
millicharge that can form electrically neutral bound states via the exchange of
a massive dark photon. If bound state formation is suppressed at low
temperatures, a sub-dominant fraction of millicharged particles remains at late
times, which can give rise to interesting features in the 21 cm absorption
profile at cosmic dawn. The dominant neutral component, on the other hand, can
have dipole interactions with ordinary matter, leading to non-standard signals
in direct detection experiments. We identify the parameter regions predicting a
percent-level ionisation fraction and study constraints from laboratory
searches for dark matter scattering and dark photon decays.

30
The categories of this paper are: q-alg
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
20
The categories of this paper are: acc-phys
23
The categories of this paper are: solv-int
37
The categories of this paper are: supr-con
12
The categories of this paper are: nucl-th
25
The categories of this paper are: patt-sol
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
8
The categories of this paper are: hep-ex
27
The categories of this paper are: comp-gas
14
The categories of this paper are: math-ph
1
The categories of this paper are: cs
18
The categories of this paper are: econ
3
The categories of this paper are: physics