Dissipative hidden sector dark matter

Understand

A simple way of explaining dark matter without modifying known Standard Model physics is to require the existence of a hidden (dark) sector, which interacts with the visible one predominantly via gravity.

• We consider a hidden sector containing two stable particles charged under an unbroken $U(1)^{'}$ gauge symmetry, hence featuring dissipative interactions.
• The massless gauge field associated with this symmetry, the dark photon, can interact via kinetic mixing with the ordinary photon.
• In fact, such an interaction of strength $\epsilon \sim 10 ^{-9}$ appears to be necessary in order to explain galactic structure.