130GeV gamma-ray line through axion conversion
  We apply the axion-photon conversion mechanism to the 130 GeV $\gamma$-ray
line observed by the Fermi satellite. Near the Galactic center, some
astrophysical sources and/or particle dark matter can produce energetic axions
(or axionlike particles), and the axions convert to $\gamma$ rays in Galactic
magnetic fields along their flight to the Earth. Since continuum $\gamma$-ray
and antiproton productions are sufficiently suppressed in axion production, the
scenario fits the 130 GeV $\gamma$-ray line without conflicting with cosmic ray
measurements. We derive the axion production cross section and the decay rate
of dark matter to fit the $\gamma$-ray excess as functions of axion parameters.
In the scenario, the $\gamma$-ray spatial distributions depend on both the dark
matter profile and the magnetic field configuration, which will be tested by
future $\gamma$-ray observations, e.g., H.E.S.S. II, CTA, and GAMMA-400. As an
illustrative example, we study realistic supersymmetric axion models, and show
the favored parameters that nicely fit the $\gamma$-ray excess.
