Origin of Delta N_eff as a Result of an Interaction between Dark Radiation and Dark Matter

Understand

Results from the Wilkinson Microwave Anisotropy Probe (WMAP), Atacama Cosmology Telescope (ACT) and recently from the South Pole Telescope (SPT) have indicated the possible existence of an extra radiation component in addition to the well known three neutrino species predicted by the Standard Model of particle physics.

• In this paper, we explore the possibility of the apparent extra dark radiation being linked directly to the physics of cold dark matter (CDM).
• In particular, we consider a generic scenario where dark radiation, as a result of an interaction, is produced directly by a fraction of the dark matter density effectively decaying into dark radiation.
• At an early epoch when the dark matter density is negligible, as an obvious consequence, the density of dark radiation is also very small.