Abstract
Collider searches for long-lived particles yield a promising avenue to probe the freeze-in production of Dark Matter via the decay of a parent particle. We analyze the prospects of probing the parameter space of Dark Matter freeze-in from the decay of neutral parent particles at the LHC and beyond, taking as a case study a freeze-in Dark Matter scenario via the Standard Model Higgs. We obtain the projected sensitivity of the proposed MATHUSLA surface detector (for MATHUSLA100 and MATHUSLA200 configurations) for long-lived particle searches to the freeze-in Dark Matter parameter space, and study its complementarity to searches by ATLAS and CMS at HL-LHC, as well as the interplay with constraints from Cosmology: Big-Bang Nucleosynthesis and Lyman-α forest observations. We then analyze the improvement in sensitivity that would come from a forward detector within a future 100 TeV pp-collider. In addition, we discuss several technical aspects of the present Dark Matter freeze-in scenario: the role of the electroweak phase transition; the inclusion of thermal masses, which have been previously disregarded in freeze-in from decay studies; the impact of 2 → 2 scattering processes on the Dark Matter relic abundance; and the interplay between freeze-in and super-WIMP Dark Matter production mechanisms.
Highlights
In freeze-in scenarios, DM particles are very feebly coupled to the thermal bath in the early Universe and never achieve thermal equilibrium, yet the coupling between DM and the thermal bath particles allows DM to be produced in decays and/or scatterings of bath particles.1 Through these processes, the DM abundance slowly increases towards equilibrium, without ever reaching it
We show in figure 1 the DM relic density curve for m1 = 12 KeV as computed with micrOMEGAs5.0 [49]; since roughly all parameter space below this curve is excluded by the Lyman-α bound from Cosmology, figure 1 highlights that, in order to obtain the observed DM relic abundance, BR(ψ± → W ±χ1) 0.1 for m2 < 1 TeV is needed in the present freeze-in scenario
Collider searches for long-lived particles (LLPs) have been recently regarded as possible probes of DM freeze-in production via the decay of a parent particle which is accessible at colliders
Summary
We review here the main aspects of freeze-in production of DM through the decay of a parent particle A in thermal equilibrium with the plasma [8]. (after reheating at the end of inflation) the DM abundance is assumed to be negligibly small and subsequently increases continuously as the parent particle A within the thermal bath decays into DM during the radiation-dominated era.. (after reheating at the end of inflation) the DM abundance is assumed to be negligibly small and subsequently increases continuously as the parent particle A within the thermal bath decays into DM during the radiation-dominated era.4 This DM production process is effective as long as the parent particle is relativistic. As the temperature of the radiation bath drops below the mass of A, the abundance of the parent particle becomes exponentially suppressed and the DM production process ceases to be effective. In the following we consider BSM in eq (2.1) to be the SM Higgs [29, 32, 43]
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