  Dark matter or violations of the Einstein equivalence principle influence the
motion of atoms, their internal states as well as electromagnetic fields, thus
causing a signature in the signal of atomic detectors. To model such new
physics, we introduce dilaton fields and study the modified propagation of
light used to manipulate atoms in light-pulse atom interferometers. Their
interference signal is dominated by the matter's coupling to gravity and the
dilaton. Even though the electromagnetic field contributes to the phase, no
additional dilaton-dependent effect can be observed. However, the light's
propagation in gravity enters via a modified momentum transfer and its finite
speed. For illustration, we discuss effects from light propagation and the
dilaton on different atom-interferometric setups, including gradiometers,
equivalence principle tests, and dark matter detection.
