Producing Dark Matter at Particle Accelerators: Extending the landscape and performing global fits of Light Dark Matter theories

Licentiate thesis, 2024

There is overwhelming evidence for the existence of an unknown and dark mass in the universe from several different observations. This missing mass has been coined dark matter (DM), with one hypothesis being that its nature is a new type of particle which interacts minimally with ordinary matter.
Major experimental efforts attempting to search for interactions between DM and ordinary matter are currently in place, with no convincing evidence of discovery so far. These experiments have largely been geared for DM with masses O(GeV-TeV), with the main search channel being nuclear recoils from DM scattering. However, DM with lighter masses, O(MeV-GeV), have been gaining significant interest recently since they can account for the measured cosmological DM relic abundance while evading nuclear recoil direct detection constraints.
Since such light DM does not carry enough momentum to be probed optimally via nuclear recoils, other search strategies such as direct detection via electron recoils and accelerators are ideal for this mass range.

Here we study the vast theory potential of accelerator based experiments, in particular fixed target experiments, on motivated sub-GeV DM models.
In Paper I, we consider two theoretical frameworks for spin-1 sub-GeV DM, so called simplified and SIMP models, both of which are testable by current and future experiments such as the upcoming (Light Dark Matter eXperiment) LDMX. We find that simplified models are subject to strong bounds from experiments, cosmological observations, and unitarity. However SIMPs, a more sophisticated framework for spin-1 DM, are not subject to unitarity violations and current experimental constraints, while being consistent with the relic abundance measurement and in reach of near future experimental sensitivities.

There is a growing number of constraints from laboratory experiments and astrophysical and cosmological observations on sub-GeV DM, each giving information on the viable parameter space not yet excluded. In Paper II, we compare these observations with the predictions of two sub-GeV DM models (Dirac fermion and complex scalar DM). We perform this comparison within frequentist and Bayesian global analyses using the Global And Modular BSM Inference Tool (GAMBIT) extended in this work. We infer the regions of parameter space preferred by current data, and compare with projections of near future experiments.