Anatomy of Coannihilation with a Scalar Top Partner

We investigate a simplified model of dark matter where a Majorana fermion $χ$ coannihilates with a colored scalar top partner $\tilde{t}$. We explore the cosmological history, with particular emphasis on the most relevant low-energy parameters: the mass splitting between the dark matter and the coannihilator, and the Yukawa coupling $y_χ$ that connects these fields to the Standard Model top quarks. We also allow a free quartic coupling $λ_h$ between a pair of Higgs bosons and $\tilde{t}$ pairs. We pay special attention to the case where the values take on those expected where $\tilde{t}$ corresponds to the superpartner of the right-handed top, and $χ$ is a bino. Direct detection, indirect detection, and colliders are complementary probes of this simple model.

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