Stop Coannihilation in the CMSSM and SubGUT Models

Understand

Stop coannihilation may bring the relic density of heavy supersymmetric dark matter particles into the range allowed by cosmology.

• The efficiency of this process is enhanced by stop-antistop annihilations into the longitudinal (Goldstone) modes of the $W$ and $Z$ bosons, as well as by Sommerfeld enhancement of stop annihilations and the effects of bound states.
• Since the couplings of the stops to the Goldstone modes are proportional to the trilinear soft supersymmetry-breaking $A$-terms, these annihilations are enhanced when the $A$-terms are large.
• However, the Higgs mass may be reduced below the measured value if the $A$-terms are too large.