Particle Physics

The matter power spectrum on subgalactic scales is very weakly constrained so far. While inflation predicts a nearly scale-invariant primordial power spectrum down to very small scales, many new physics scenarios can lead to significantly different predictions, such as axion dark matter in the post-inflationary scenario, vector dark matter produced during inflation, early matter domination, kinetic misalignment axions, self-interacting dark matter, atomic dark matter, etc. Therefore, any successful measurement on the matter power spectrum tests inflation extensively and probes early universe dynamics and the nature of dark matter, making it a new frontier in cosmology and dark matter physics. We proposed observing fast radio bursts (FRB) with solar-system scale interferometry by sending radio telescopes to space, which allows us to greatly expand the sensitivity on the matter power spectrum from Mpc to AU scales. Two sightlines looking at the same FRB source can sample different regions of the Universe in the transverse direction and thus obtain an arrival time difference that depends on the matter power spectrum. Our calculations show that this setup will be sensitive to the scale-invariant power spectrum predicted by inflation on small scales and can also probe QCD axion miniclusters predicted in the post-inflationary scenario.

Dark matter particle interactions could imprint characteristic signals in cosmic-ray and multi-wavelength observations of the sky. The central challenge is to distinguish these signatures from similar spectra produced by standard astrophysical processes, such as the life and death of stars and the interactions of cosmic rays with interstellar material. The GAPS Antarctic balloon payload, en route for its initial flight in December 2024, is the first experiment optimized specifically for low-energy cosmic antideuterons, an essentially background-free signature of dark matter, as well as antiprotons in an unprecedented low-energy region and leading sensitivity to cosmic anithelium. In this talk, I will detail the novel GAPS detection technique, its flight instrument, and the potential impact of these measurements in the coming years. 

Primordial black hole (PBH) dark matter can be probed by "picolensing". Widely spatially separated gamma-ray detectors near Earth would observe parallax of an intervening PBH lens with respect to a cosmologically distant gamma-ray burst (GRB). This parallax can be of order the Einstein angle of the lens, resulting in differential magnification of the source as viewed from the two detectors. Simultaneous brightness measurements of the same GRB made by two detectors is sensitive to this effect. Two recent studies in the literature have shown this approach could be a promising way to search for PBH dark matter in part of the "asteroid mass window", roughly (few) * 1e-15 < M_{PBH} / M_{Sun} < (few) * 1e-11. In this talk, I will discuss some ongoing work to explore the robustness of this signal to various uncertainties not previously carefully accounted for: e.g., uncertainties in the transverse extent of the GRB emission region, its intensity profile, detector background rates, sensitivity of the projection to outlier GRB events, etc. I'll show that, while the large GRB source size uncertainties do degrade previous projections somewhat, it is still possible to probe most of the PBH DM asteroid mass window with a mission that employs two Swift/BAT-class detectors separated by a distance on the order of an AU. Depending on the total number of GRBs that such a mission ultimately observes, it may even be possible to robustly probe new subcomponent dark-matter parameter space at PBH masses above the window, potentially as high as (few) * 1e-6 M_{Sun}.