  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.
