Abstract
Displaced vertices at colliders, arising from the production and decay of long-lived particles, probe dark matter candidates produced via freeze-in. If one assumes a standard cosmological history, these decays happen inside the detector only if the dark matter is very light because of the relic density constraint. Here, we argue how displaced events could very well point to freeze-in within a non-standard early universe history. Focusing on the cosmology of inflationary reheating, we explore the interplay between the reheating temperature and collider signatures for minimal freeze-in scenarios. Observing displaced events at the LHC would allow to set an upper bound on the reheating temperature and, in general, to gather indirect information on the early history of the universe.
Highlights
Detecting non-gravitational interactions of dark matter (DM) has been the target of a vast and diverse experimental effort with no conclusive evidence so far [1,2,3]
We can still learn something about the early universe, and in particular extract an upper bound on TR, from a displaced event
In uniform green we display the reach of the recent Displaced leptons (DL) ATLAS analysis [70]
Summary
Detecting non-gravitational interactions of dark matter (DM) has been the target of a vast and diverse experimental effort with no conclusive evidence so far [1,2,3]. The main characters of our study are Feebly Interacting Massive Particles (FIMPs), new stable degrees of freedom beyond the Standard Model (SM) that never achieve thermal equilibrium through the expansion history of our universe. They are viable DM candidates since decays and/or scatterings of primordial bath particles can produce FIMPs that free-stream subsequently. If FIMP interactions are renormalizable their production is most efficient at temperatures around the mass of the heaviest particle involved in the process [6,7,8,9]. The resulting relic density depends only on masses and couplings that we can measure in our laboratories and/or astrophysically and this “IR-dominated” production mechanism has been dubbed freeze-in in the literature [9]
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