Gravitational Dark Matter Decay and the ATIC/PPB-BETS Excess
  The hidden scalar field, which couples to the visible sector only through
Planck-suppressed interactions, is a candidate for dark matter owing to its
long lifetime. Decay of such a scalar field offers observational tests of this
scenario. We show that decay of the hidden scalar field can explain the
observed excess of high-energy positrons/electrons observed by ATIC/PPB-BETS,
for a suitable choice of the mass and the vacuum expectation value of the
field. We also show that the same choice of the parameters gives the observed
dark matter abundance. Such a remarkable coincidence suggests that the
Planck-suppressed interactions may be responsible for the observed excess in
the cosmic-ray positrons/electrons.
