After reionize the surrounding IGM . However, as the scattering cross section of photons with energies near that of the Lyman-alpha limit with neutral hydrogen is very high, even a small fraction of neutral hydrogen will make the optical depth of the IGM high enough to cause the suppression of emission observed.
32.
Generally PMSE exhibits dramatic variations in height and intensity as well as large variations in Doppler shift . PMSE exhibit strong signal power enhancements of scattering cross section at VHF radar frequencies in the range 50 MHz to 250 MHz, at times even to over 1 GHz, that occur in summer at high latitudes.
33.
Light-by-light scattering can be studied using the strong electromagnetic fields of the hadrons collided at the LHC, it has first been seen in 2016 by the LHC . The best previous constraint on the elastic photon photon scattering cross section was set by PVLAS, which reported an upper limit far above the level predicted by the Standard Model.
