Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gamma Lines without a Continuum: Thermal Models for the Fermi-LAT 130
  GeV Gamma Line   Recent claims of a line in the Fermi-LAT photon spectrum at 130 GeV are
suggestive of dark matter annihilation in the galactic center and other dark
matter-dominated regions. If the Fermi feature is indeed due to dark matter
annihilation, the best-fit line cross-section, together with the lack of any
corresponding excess in continuum photons, poses an interesting puzzle for
models of thermal dark matter: the line cross-section is too large to be
generated radiatively from open Standard Model annihilation modes, and too
small to provide efficient dark matter annihilation in the early universe. We
discuss two mechanisms to solve this puzzle and illustrate each with a simple
reference model in which the dominant dark matter annihilation channel is
photonic final states. The first mechanism we employ is resonant annihilation,
which enhances the annihilation cross-section during freezeout and allows for a
sufficiently large present-day annihilation cross section. Second, we consider
cascade annihilation, with a hierarchy between p-wave and s-wave processes.
Both mechanisms require mass near-degeneracies and predict states with masses
closely related to the dark matter mass; resonant freezeout in addition
requires new charged particles at the TeV scale.

29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
4
The categories of this paper are: cond-mat
33
The categories of this paper are: plasm-ph
21
The categories of this paper are: adap-org
25
The categories of this paper are: patt-sol
3
The categories of this paper are: physics
34
The categories of this paper are: chem-ph
8
The categories of this paper are: hep-ex
23
The categories of this paper are: solv-int
32
The categories of this paper are: atom-ph
35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
5
The categories of this paper are: gr-qc
24
The categories of this paper are: dg-ga
9
The categories of this paper are: nlin