  We propose a model in which an energy-dependent time delay of a photon
originates from space-time non-commutativity, the time delay is due to a
noncommutative coupling between dilaton and photon. We predict that in our
model, high energy photons with different momenta can either be delayed or
superluminal, this may be related to a possible time delay reported by the
Fermi LAT and Fermi GBM Collaborations.
