Calculations of neutralino-stop coannihilation in the CMSSM

We present detailed calculations of the X̃t̃ ₁ coannihilation channels that have the largest impact on the relic ̃X density in the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which scalar masses m ₀ , gaugino masses m _1/2 and the trilinear soft supersymmetry-breaking parameters A ₀ are each assumed to be universal at some input grand unification scale. The most important t̃ ₁ t̃ ₁ * and t̃ ₁ t̃ ₁ annihilation channels are also calculated, as well as t̃ ₁ ̃el coannihilation channels. We illustrate the importance of these new coannihilation calculations when A ₀ is relatively large. While they do not increase the range of m _1/2 and hence m _χ allowed by cosmology, these coannihilation channels do open up new 'tails' of parameter space extending to larger values of m ₀ .