Calculations of neutralino-stop coannihilation in the CMSSM

We present detailed calculations of the χ̃t̃1 coannihilation channels that have the largest impact on the relic χ̃ density in the constrained minimal supersymmetric extension of the Standard Model (CMSSM), in which scalar masses m0, gaugino masses m1/2 and the trilinear soft supersymmetry-breaking parameters A0 are each assumed to be universal at some input grand unification scale. The most important t̃1t̃1∗ and t̃1t̃1 annihilation channels are also calculated, as well as t̃1ℓ̃ coannihilation channels. We illustrate the importance of these new coannihilation calculations when A0 is relatively large. While they do not increase the range of m1/2 and hence mχ allowed by cosmology, these coannihilation channels do open up new ‘tails’ of parameter space extending to larger values of m0.