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A thermal relic, often referred to as a weakly interacting massive particle(WIMP), is a particle produced during the early evolution of the Universe whosepresent (relic) abundance depends only on its mass and its thermally averagedannihilation cross section (annihilation rate factor) sigma*v_ann. Late timeWIMP annihilation has the potential to affect the cosmic microwave background(CMB) power spectrum. Current observational constraints on the absence of sucheffects provide bounds on the mass and the annihilation cross section of relicparticles that may, but need not be dark matter candidates. For a WIMP that isa dark matter candidate, the CMB constraint sets an upper bound to theannihilation cross section, leading to a lower bound to its mass that dependson whether or not the WIMP is its own antiparticle. For a self-conjugate WIMP,m_min = 50f GeV, where f is an electromagnetic energy efficiency factor. For anon self-conjugate WIMP, the minimum mass is a factor of two larger. For a WIMPthat is a subdominant component of the dark matter density there is no bound onits mass and the upper bound to its annihilation cross section imposed by theCMB transforms into a lower bound to its annihilation cross section. Theseresults are outlined and quantified here using the latest CMB constraints for astable, symmetric (equal number of particles and antiparticles), WIMP whoseannihilation is s-wave dominated, and for particles that are, or are not, theirown antiparticle.

CMB Constraints On The Thermal WIMP Mass And Annihilation Cross Section