  In this paper, we review the approach leading to cosmic polarization rotation
observation and present the current status with an outlook. In the study of the
relations among equivalence principles, we found that long-range
pseudoscalar-photon interaction is allowed. Pseudoscalar-photon interaction
would induce a rotation of linear polarization of electromagnetic wave
propagating with cosmological/astrophysical distance. In 2002, DASI
successfully observed the polarization of the cosmological microwave background
radiation. In 2003, WMAP observed the correlation of polarization with
temperature anisotropy at more than 10 sigma in the cosmological microwave
background. From this high polarization-temperature correlation in WMAP
observation, we put a limit of 0.1 rad on the rotation of linear polarization
of cosmological microwave background (CMB) propagation. Pseudoscalar-photon
interaction is proportional to the gradient of the pseudoscalar field. From
phenomenological point of view, this gradient could be neutrino number
asymmetry current, other density current, or a constant vector. In these
situations, Lorentz invariance or CPT may or may not effectively be violated.
In this paper, we review and compile various results. Better accuracy in CMB
polarization observation is expected from PLANCK mission to be launched next
year. A dedicated CMB polarization observer in the future would probe this
fundamental issue more deeply.
