Super-horizon Perturbations and CMBA
  We provided a gedanken experiment and argued that since observers inside a given Hubble volume could not detect the super horizon perturbation modes as real perturbations, these modes could only affect the average value of the cosmic microwave background (CMB), but not its anisotropy properties (CMBA) in that Hubble volume. 
Ding-fang Zeng and Yi-hong Gao