Calculations of Neutralino-Stop Coannihilation in the CMSSM

We present detailed calculations of the neutralino-stop coannihilation channels that have the largest impact on the relic neutralino 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 stop-stop* and stop-stop annihilation channels are also calculated, as well as stop-slepton 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 neutralino mass allowed by cosmology, these coannihilation channels do open up new `tails' of parameter space extending to larger values of m_0.