A Dark Matter Hurricane: Measuring the S1 Stream with Dark Matter Detectors

The recently discovered S1 stream passes through the Solar neighbourhood on a low inclination, counter-rotating orbit. The progenitor of S1 is a dwarf galaxy with a total mass comparable to the present-day Fornax dwarf spheroidal, so the stream is expected to have a significant DM component. We compute the effects of the S1 stream on WIMP and axion detectors as a function of the density of its unmeasured dark component. In WIMP detectors the S1 stream supplies more high energy nuclear recoils so will marginally improve DM detection prospects. We find that even if S1 comprises less than 10% of the local density, multi-ton xenon WIMP detectors can distinguish the S1 stream from the bulk halo in the relatively narrow mass range between 5 and 25 GeV. In directional WIMP detectors such as CYGNUS, S1 increases DM detection prospects more substantially since it enhances the anisotropy of the WIMP signal. Finally, we show that axion haloscopes possess by far the greatest potential sensitivity to the S1 stream. Once the axion mass has been discovered, the distinctive velocity distribution of S1 can easily be extracted from the axion power spectrum.Comment: 21 pages, 11 figure

Detecting WIMPs, neutrinos and axions in the next generation of dark matter experiment

The first direct detection of dark matter is anticipated in coming years by one of a range of experimental strategies. Because the identity of dark matter remains unknown, the strategy that will be successful in this one cannot say. However beneath this fundamental particle physics uncertainty lies another uncertainty with regard to the structure of the dark matter halo of the Milky Way that must be confronted when interpreting data from terrestrial experiments. However these astrophysical uncertainties might only be resolved with the very same experiments; in fact, directly detecting dark matter represents the only way to probe the ultralocal structure of the halo. This thesis explores the impact of astrophysical uncertainties on the particle physics goals of dark matter detection but also the extent to which we might in the future be able to resolve those uncertainties. The discussion is framed around the detection of three types of particle, two of which are dark matter candidates: weakly interacting massive particles (WIMPs), neutrinos and axions. In the case of WIMPs I consider how upcoming directionally sensitive experiments can be used to probe the full 3-dimensional velocity distribution to learn about dark matter substructure. A range of model dependent and independent statistical approaches are tested under various astrophysical benchmarks. I also explore prospects for WIMP direct detection when faced with the ultimate neutrino background, as expected in the next generation of experiment. In this eventuality the uncertainties in the neutrino flux are essential in predicting the WIMP models inaccessible due to the background. However the same is true of astrophysical uncertainties. Once astrophysical uncertainties are accounted for the neutrino floor limit is raised in cross section by up to an order of magnitude and the accuracy of any potential WIMP particle measurement is greatly increased. Addressing these concerns, I demonstrate how one should go about subtracting the neutrino background. This involves a return to directional detection. I find that even non-ideal circumstances, the neutrino and WIMP signals can be distinguished and the neutrino floor overcome. Finally in the context of axions, I discuss the prospects for microwave cavity haloscope experiments to perform "axion astronomy". Haloscopes measure the direct conversion of axions into photons and hence can make potentially much finer measurements of the dark matter halo compared with WIMPs. I develop a technique to extract astrophysical parameters, such as the halo velocity dispersion and laboratory velocity, as well as learn about properties of substructure from tidal streams and axion miniclusters. I show that a level of precision can be achieved in relatively short duration haloscope experiments that can match or improve upon that of astronomical observations

Eliminating the LIGO bounds on primordial black hole dark matter

Primordial black holes (PBHs) in the mass range $(30$--$100)~M_{\odot}$ are interesting candidates for dark matter, as they sit in a narrow window between microlensing and cosmic microwave background constraints. There are however tight constraints from the binary merger rate observed by the LIGO and Virgo experiments. In deriving these constraints, PBHs were treated as point Schwarzschild masses, while the more careful analysis in an expanding universe we present here, leads to a time-dependent mass. This implies a stricter set of conditions for a black hole binary to form and means that black holes coalesce much more quickly than was previously calculated, namely well before the LIGO/Virgo's observed mergers. The observed binaries are those coalescing within galactic halos, with a merger rate consistent with data. This reopens the possibility for dark matter in the form of LIGO-mass PBHs.Comment: formatting + structure updated, and some arguments have been extended and slightly rewritten for clarity. no changes to the physics or conclusion

Weighing the Solar Axion

Axion helioscopes search for solar axions and axion-like particles via inverse Primakoff conversion in strong laboratory magnets pointed at the Sun. While helioscopes can always measure the axion coupling to photons, the conversion signal is independent of the mass for axions lighter than around 0.02 eV. Masses above this value on the other hand have suppressed signals due to axion-photon oscillations which destroy the coherence of the conversion along the magnet. However, the spectral oscillations present in the axion conversion signal between these two regimes are highly dependent on the axion mass. We show that these oscillations are observable given realistic energy resolutions and can be used to determine the axion mass to within percent level accuracies. Using projections for the upcoming helioscope IAXO, we demonstrate that $>3\sigma$ sensitivity to a non-zero axion mass is possible between $3 \times 10^{-3}$ and $10^{-1}$ eV for both the Primakoff and axion-electron solar fluxes.Comment: 13 pages, 7 figures, matches published version, code available at http://cajohare.github.io/IAXOmas