PI: Will Handley

Sub-GeV dark matter particles produced via thermal freeze-out evade many constraints on heavier candidates but face a multitude of new constraints from laboratory experiments, astrophysical observations and cosmological data. In 2025, Balan, Kahlhoefer, Gonzalo et al. (arXiv:2405.17548, JCAP 01 053) used DiRAC CSD3 to perform the first comprehensive global analysis of sub-GeV dark matter using the GAMBIT framework. Combining constraints from direct detection, accelerator searches, Big Bang nucleosynthesis, the cosmic microwave background and the relic abundance, the team performed both frequentist profile likelihood and Bayesian nested sampling scans across the full parameter space of fermionic and scalar dark matter models with a dark photon mediator. The analysis required millions of CPU-hours on CSD3, scanning over 7-dimensional parameter spaces with computationally expensive likelihood evaluations at each point.

Figure: Preferred region for asymmetric fermionic sub-GeV dark matter in the mass-coupling plane, computed using GAMBIT on DiRAC CSD3. Contours show 1 and 2 sigma profile likelihood regions. Dashed lines indicate projected sensitivities of next-generation experiments. From Balan, Kahlhoefer et al. (2025).

The results identify two viable mechanisms: resonant annihilation and asymmetric dark matter, both making sharp predictions for next-generation experiments (SENSEI, DAMIC, LDMX; see Figure). Follow-up studies extended this to classically conformal dark sectors and gravitational waves (Balan & Kahlhoefer, arXiv:2502.19478, JCAP 08 062) and reassessed the DAMA/LIBRA claim (Kvellestad et al., arXiv:2510.05216).