Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Astrophysical constraints on millicharged atomic dark matter   Some models of inelastic dark matter posit the existence of bound states
under some new $U(1)'$ gauge symmetry. If this new dark photon kinetically
mixes with the standard model photon, then the constituent particles in these
bound states can acquire a fractional electric charge. This electric charge
renders a dark-matter medium dispersive. We compute this frequency-dependent
index of refraction for such a medium and use the frequency-dependent arrival
time of light from astrophysical sources to constrain the properties of dark
atoms in the medium. Using optical-wavelength observations from the Crab
Pulsar, we find the electric millicharge of dark (electrons) protons to be
smaller than the electric charge $e$ for dark atom masses below 100 keV,
assuming a dark fine structure constant $\boldsymbol{\alpha}=1$. We estimate
that future broadband observations of gamma-ray bursts can produce constraints
on the millicharge of dark atoms with masses in the keV range that are
competitive with existing collider constraints.

18
The categories of this paper are: econ
3
The categories of this paper are: physics
2
The categories of this paper are: math
37
The categories of this paper are: supr-con
32
The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
12
The categories of this paper are: nucl-th
24
The categories of this paper are: dg-ga
14
The categories of this paper are: math-ph
6
The categories of this paper are: astro-ph
35
The categories of this paper are: mtrl-th
33
The categories of this paper are: plasm-ph
13
The categories of this paper are: quant-ph
28
The categories of this paper are: alg-geom
34
The categories of this paper are: chem-ph
4
The categories of this paper are: cond-mat