Dark Matter with Density-Dependent Interactions

Understand

The decay and annihilation cross sections of dark matter particles may depend on the value of a chameleonic scalar field that both evolves cosmologically and takes different values depending on the local matter density.

• This possibility introduces a separation between the physics relevant for freeze-out and that responsible for dynamics and detection in the late universe.
• We investigate how such dark sector interactions might be implemented in a particle physics Lagrangian and consider how current and upcoming observations and experiments bound such dark matter candidates.
• A specific simple model allows for an increase in the annihilation cross section by a factor of $10^6$ between freeze-out and today, while more complicated models should also allow for scattering cross sections near the astrophysical bounds.