Chameleon-Photon Mixing in a Primordial Magnetic Field

Understand

We consider the non-resonant mixing between photons and scalar ALPs with masses much less than the plasma frequency along the path, with specific reference to the chameleon scalar field model.

• The mixing would alter the intensity and polarization state of the cosmic microwave background (CMB) radiation.
• We find that the average modification to the CMB polarization modes is negligible.
• However the average modification to the CMB intensity spectrum is more significant and we compare this to high precision measurements of the CMB monopole made by the far infrared absolute spectrophotometer (FIRAS) on board the COBE satellite.