A Hidden Dark Matter Sector, Dark Radiation, and the CMB

Understand

We consider theories where dark matter is composed of a thermal relic of weak scale mass, whose couplings to the Standard Model (SM) are however too small to give rise to the observed abundance.

• Instead, the abundance is set by annihilation to light hidden sector states that carry no charges under the SM gauge interactions.
• In such a scenario the constraints from direct and indirect detection, and from collider searches for dark matter, can easily be satisfied.
• The masses of such light hidden states can be protected by symmetry if they are Nambu-Goldstone bosons, fermions, or gauge bosons.