guska'u lujvo

x1 is a photon.

Cf. gusni, kantu, lektoni, kuarka.

In notes:

x1 is an electron in quantum state x2
x1 is a quark with flavor x2.
x1 emits light characteristic of/is of the color that is described by/(as) arising from/associated with the approximately twenty-one centimeter wavelength, hydrogen hyperfine proton/electron spin-flip transition (from parallel to antiparallel configuration, id est: from the higher energy state to the lower energy state), electromagnetic radiation