Schematic drawing of a representative emission process (left), and the corresponding Feynman diagram (right). The photon lives in 3D space, while the electrons are confined to the graphene sheet. The initial electron is described by its momentum and its pseudospin, which for a conduction electron near is directed along. Interacting with the photon (wavevector and polarization) destroys the conduction electron, creating a valence band electron with momentum and pseudospin.