The Extent of the Stop Coannihilation Strip

Many supersymmetric models such as the CMSSM feature a strip in parameter space where the lightest neutralino \chi is identified as the lightest supersymmetric particle (LSP), the lighter stop squark \tilde t_1 is the next-to-lightest supersymmetric particle (NLSP), and the relic \chi cold dark matter density is brought into the range allowed by astrophysics and cosmology by coannihilation with the lighter stop squark \tilde t_1 NLSP. We calculate the stop coannihilation strip in the CMSSM, incorporating Sommerfeld enhancement effects, and explore the relevant phenomenological constraints and phenomenological signatures. In particular, we show that the \tilde t_1 may weigh several TeV, and its lifetime may be in the nanosecond range, features that are more general than the specific CMSSM scenarios that we study in this paper.