When radiation is important, the particles undergo radiation damping ( which slowly decreases emittance turn after turn ) and quantum excitation causing diffusion which leads to an equilibrium emittance.
2.
The fundamental geometric idea of E 8 Theory is that our universe and its contents exists as quantum excitations of the largest simple real quaternionic exceptional Lie group, " E " 8 ( " 24 ).
3.
Yes, photon says the slowing down is due to " blending of the photon with quantum excitation of the matter ( quasi-particles such as phonons and excitons ) to form a polariton; this polariton has a nonzero effective mass ".
4.
The goal of E 8 Theory is to describe all elementary particles and their interactions, including gravitation, as quantum excitations of a single Lie group geometry specifically, excitations of the noncompact quaternionic real form of the largest simple exceptional Lie group, representation.