Abstract
We re-examine the stop co-annihilation scenario of the Minimal Supersymmetric Standard Model, wherein a bino-like lightest supersymmetric particle has a thermal relic density set by co-annihilations with a scalar partner of the top quark in the early universe. We concentrate on the case where only the top partner sector is relevant for the cosmology, and other particles are heavy. We discuss the cosmology with focus on low energy parameters and an emphasis on the implications of the measured Higgs boson mass and its properties. We find that the irreducible direct detection signal correlated with this cosmology is generically well below projected experimental sensitivity, and in most cases lies below the neutrino background. A larger, detectable, direct detection rate is possible, but is unrelated to the co-annihilation cosmology. LHC searches for compressed spectra are crucial for probing this scenario.
Highlights
The Minimal Supersymmetric Standard Model (MSSM) is a leading candidate for physics beyond the Standard Model (SM)
As we showed in the previous section, the mass splitting necessary to reproduce the thermal relic density is much smaller than the top mass independently of whether the next to lightest supersymmetric particle (NLSP)
We have revisited the stop co-annihilation scenario wherein dark matter freeze-out, stopinduced corrections to the Higgs boson mass as well as an irreducible direct detection cross section mediated by stop/sbottom loops are interrelated
Summary
The Minimal Supersymmetric Standard Model (MSSM) is a leading candidate for physics beyond the Standard Model (SM). Crossing symmetry is spoiled if the dark matter coinhabits the thermal bath with another exotic state at the time of freeze-out [5] Processes involving this co-annihilating partner can be important for the determination of the relic density, but are unrelated (at tree level) to direct detection. [6,7,8,9] because there are typically a small number of processes that dominate the cosmology involving only a handful of particles and couplings, it is illuminating to analyze these models in terms of the low energy parameters Consistent with this approach, in previous work [10] we considered the possibility where a single top partner (perhaps the superpartner of the right-handed top) was responsible for co-annihilation, see Refs.
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