Conversion of Gravitons into Dark Photons in Cosmological Dark Magnetic
  Fields
  It is well known that gravitons can convert into photons, and vice versa, in
the presence of cosmological magnetic fields. We study this conversion process
in the context of atomic dark matter scenario. In this scenario, we can expect
cosmological dark magnetic fields, which are free from the stringent constraint
from the cosmic microwave observations. We find that gravitons can effectively
convert into dark photons in the presence of cosmological dark magnetic fields.
The graviton-dark photon conversion effect may open up a new window for ultra
high frequency gravitational waves.
