Dilaton field and cosmic wave propagation
  We study the electromagnetic wave propagation in the joint dilaton field and axion field. Dilaton field induces amplification/attenuation in the propagation while axion field induces polarization rotation. The amplification/attenuation induced by dilaton is independent of the frequency (energy) and the polarization of electromagnetic waves (photons). From observations, the agreement with and the precise calibration of the cosmic microwave background (CMB) to blackbody radiation constrains the fractional change of dilaton |{\Delta}{\psi}|/{\psi} to less than about 8 x 10^(-4) since the time of the last scattering surface of the CMB. 
Wei-Tou Ni
gr-qc astro-ph.CO hep-ph physics.optics