https://en.wikipedia.org/wiki/Photon
extract:
The photon as a gauge boson[edit]
Main article:
Gauge theory
The electromagnetic field can be understood as a
gauge field, i.e., as a field that results from requiring that a gauge symmetry holds independently at every position in
spacetime.
[102]For the
electromagnetic field, this gauge symmetry is the
Abelian U(1) symmetry of
complex numbers of absolute value 1, which reflects the ability to vary the
phase of a complex field without affecting
observables or
real valued functions made from it, such as the
energy or the
Lagrangian.
The quanta of an
Abelian gauge field must be massless, uncharged bosons, as long as the symmetry is not broken; hence, the photon is predicted to be massless, and to have zero
electric charge and integer spin. The particular form of the
electromagnetic interaction specifies that the photon must have
spin ±1; thus, its
helicity must be {\displaystyle \pm \hbar }
. These two spin components correspond to the classical concepts of
right-handed and left-handed circularly polarized light. However, the transient
virtual photons of
quantum electrodynamics may also adopt unphysical polarization states.
[102]
In the prevailing
Standard Model of physics, the photon is one of four
gauge bosons in the
electroweak interaction; the
other three are denoted W+, W− and Z0 and are responsible for the
weak interaction. Unlike the photon, these gauge bosons have
mass, owing to a
mechanismthat breaks their
SU(2) gauge symmetry. The unification of the photon with W and Z gauge bosons in the electroweak interaction was accomplished by
Sheldon Glashow,
Abdus Salamand
Steven Weinberg, for which they were awarded the 1979
Nobel Prize in physics.
[103][104][105] Physicists continue to hypothesize
grand unified theories that connect these four
gauge bosons with the eight
gluon gauge bosons of
quantum chromodynamics; however, key predictions of these theories, such as
proton decay, have not been observed experimentally