A dark photon is a hypothetical elementary particle that mediates a new long-range force similar to electromagnetism. The dark photon would be electrically neutral and have very weak interactions with ordinary matter. It is predicted by some extensions of the Standard Model of particle physics, such as string theory, and could explain certain observations that are otherwise unexplained, such as the apparent lack of antimatter in the universe.
If it exists, the dark photon would be part of a new “hidden” or “dark” sector of particles that do not interact with the known particles of the Standard Model. This hidden sector might also contain other hypothetical particles such as dark atoms and black holes. The existence of a dark photon could help to explain why the known particles seem to be arranged in three generations (with each generation consisting of two quarks and an lepton), rather than just one or two generations. It might also help to explain why there is more matter than antimatter in the universe, as well as providing a possible solution to the so-called “missing mass” problem in cosmology.
The most direct way to search for the dark photon is through its interaction with ordinary matter via its mixing with the regular electromagnetic field. This mixing can be searched for in laboratory experiments using lasers or microwave cavities, or by looking for anomaly in electron electric dipole moment measurements. Indirect searches for signs of new physics associated with a hidden sector can also be made by studying cosmic ray collisions or astronomical objects such as gamma-ray binaries.