Abstract
We analyze the sensitivity of fixed-target experiments to sub-GeV thermal relic dark matter models, accounting for variations in both mediator and dark matter mass, and including dark matter production through both on- and off-shell mediators. It is commonly thought that the sensitivity of such experiments is predicated on the existence of an on-shell mediator that is produced and then decays to dark matter. While accelerators do provide a unique opportunity to probe the mediator directly, our analysis demonstrates that their sensitivity extends beyond this commonly discussed regime. In particular, we provide sensitivity calculations that extend into both the effective field theory regime where the mediator is much heavier than the dark matter and the regime of an off-shell mediator lighter than a dark matter particle-antiparticle pair. Our calculations also elucidate the resonance regime, making it clear that all but a fine-tuned region of thermal freeze-out parameter space for a range of simple models is well covered.
Highlights
The evidence for a dark matter (DM) component in the universe, through its gravitational effects over many distance scales, provides the strongest indicator to-date for physics beyond the Standard Model (SM)
Theoretical and experimental approaches to particle DM have evolved significantly, with a loosening of theoretical priors about how DM may be explained within particle physics
This has been driven on the one hand by the increasingly stringent LHC constraints on new TeV-scale degrees of freedom, and on the other by the recognition that the strong empirical evidence for DM motivates exploring all viable and testable scenarios for DM, not just those that are linked to other expectations for new physics [e.g., the naturalness problem motivating electroweak-scale weakly interacting massive particles (WIMPs), or the strong CP problem motivating axions]
Summary
The evidence for a dark matter (DM) component in the universe, through its gravitational effects over many distance scales, provides the strongest indicator to-date for physics beyond the Standard Model (SM). Theoretical and experimental approaches to particle DM have evolved significantly, with a loosening of theoretical priors about how DM may be explained within particle physics This has been driven on the one hand by the increasingly stringent LHC constraints on new TeV-scale degrees of freedom, and on the other by the recognition that the strong empirical evidence for DM motivates exploring all viable and testable scenarios for DM, not just those that are linked to other expectations for new physics [e.g., the naturalness problem motivating electroweak-scale weakly interacting massive particles (WIMPs), or the strong CP problem motivating axions]. Motivated by models of light DM, much theoretical and experimental effort over the past decade has focused on the vector portal, which at low energies involves kinetic mixing between the photon and the dark vector, ðε=2ÞFμνF0μν This is in part because it is the least constrained scenario that allows for bilinear mixing. For fermionic DM χ coupled to SM vector currents, the leading interactions are typically of the form
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