CMB Constraints On The Thermal WIMP Mass And Annihilation Cross Section

Understand

A thermal relic, often referred to as a weakly interacting massive particle (WIMP), is a particle produced during the early evolution of the Universe whose present (relic) abundance depends only on its mass and its thermally averaged annihilation cross section (annihilation rate factor) sigma*v_ann.

• Late time WIMP annihilation has the potential to affect the cosmic microwave background (CMB) power spectrum.
• Current observational constraints on the absence of such effects provide bounds on the mass and the annihilation cross section of relic particles that may, but need not be dark matter candidates.
• For a WIMP that is a dark matter candidate, the CMB constraint sets an upper bound to the annihilation cross section, leading to a lower bound to its mass that depends on whether or not the WIMP is its own antiparticle.