Abstract
We present a comprehensive analysis of top-philic Majorana dark matter that interacts via a colored t-channel mediator. Despite the simplicity of the model -- introducing three parameters only -- it provides an extremely rich phenomenology allowing us to accommodate the relic density for a large range of coupling strengths spanning over six orders of magnitude. This model features all `exceptional' mechanisms for dark matter freeze-out, including the recently discovered conversion-driven freeze-out mode, with interesting signatures of long-lived colored particles at colliders. We constrain the cosmologically allowed parameter space with current experimental limits from direct, indirect and collider searches, with special emphasis on light dark matter below the top mass. In particular, we explore the interplay between limits from Xenon1T, Fermi-LAT and AMS-02 as well as limits from stop, monojet and Higgs invisible decay searches at the LHC. We find that several blind spots for light dark matter evade current constraints. The region in parameter space where the relic density is set by the mechanism of conversion-driven freeze-out can be conclusively tested by R-hadron searches at the LHC with 300\,fb$^{-1}$.
Highlights
Astrophysical and cosmological probes continue to consolidate our knowledge of the gravitational impact of dark matter (DM)
In this work we presented a comprehensive phenomenological study of a simplified DM model where a neutral Majorana fermion is responsible for the observed DM abundance and interacts via a top-philic t-channel scalar mediator
We find that this setup comprises a complex but well-defined phenomenology, giving rise to a large amount and distinct combination of signatures, some of which go beyond those for typical weakly interacting massive particle (WIMP) searches
Summary
Astrophysical and cosmological probes continue to consolidate our knowledge of the gravitational impact of dark matter (DM) (see e.g. [1,2]). For coupling strengths in the ballpark of the SM gauge couplings the relic density can be generated by DM freeze-out with or without strong coannihilation effects depending on the mass splitting between the DM and the mediator. In this region DM shares the properties of a weakly interacting massive particle (WIMP). The phenomenological consequences are striking: The parameter region accommodating the measured relic density via conversion-driven freeze-out cannot be probed by conventional WIMP searches but predicts new signatures of longlived particles at colliders [30].
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