  Monochromatic gamma-ray lines are thought to be the smoking gun signal of the
annihilation or decay of dark matter since they do not suffer from deflection
or absorption on galactic scales. A recent claim on strong evidence for two
gamma-ray lines from the inner galaxy suggests that two-body final states might
be one photon plus a Z boson or one photon plus a Higgs boson. In this study,
we investigate which final state is more possible by analyzing the energy
resolution of the Fermi-LAT. It is concluded that the former case, i.e. one
photon plus a Z boson is more plausible than the latter one, i.e. one photon
and a Higgs boson since in the latter case the mass of dark matter particle
shows tension with a constraint coming from the energy resolution of the
Fermi-LAT.
