Daniel T. Cumberbatch

Sterile neutrinos as subdominant warm dark matter

In light of recent findings which seem to disfavor a scenario with (warm) dark matter entirely constituted of sterile neutrinos produced via the Dodelson-Widrow mechanism, we investigate the constraints attainable for this mechanism by relaxing the usual hypothesis that the relic neutrino abundance must necessarily account for all of the dark matter. We first study how to reinterpret the limits attainable from x-ray nondetection and Lyman-{alpha} forest measurements in the case that sterile neutrinos constitute only a fraction f{sub s} of the total amount of dark matter. Then, assuming that sterile neutrinos are generated in the early universe solely through the Dodelson-Widrow mechanism, we show how the x-ray and Lyman-{alpha} results jointly constrain the mass-mixing parameters governing their production. Furthermore, we show how the same data allow us to set a robust upper limit f{sub s} < or approx. 0.7 at the 2{sigma} level, rejecting the case of dominant dark matter (f{sub s}=1) at the {approx}3{sigma} level.

Light WIMPs in the Sun: Constraints from Helioseismology

We calculate solar models including dark matter (DM) weakly-interacting massive particles (WIMPs) of mass 5-50 GeV and test these models against helioseismic constraints on sound speed, convection zone depth, convection zone helium abundance, and small separations of low-degree pmodes. Our main conclusion is that both direct detection experiments and particle accelerators may be complemented by using the Sun as a probe for WIMP DM particles in the 5-50 GeV mass range. The DM most sensitive to this probe has suppressed annihilations and a large spin-dependent elastic scattering cross section. For the WIMP cross-section parameters explored here, the lightest WIMP masses < 10 GeV are ruled out by constraints on core sound speed and low-degree frequency spacings. For WIMP masses 30-50 GeV, the changes to the solar structure are conned to the inner 4% of the solar radius and so do not signicantly aect the solar p-modes. Future helioseismology observations, most notably involving g-modes, and future solar neutrino experiments may be able to constrain the allowable DM parameter space in a mass range that is of current interest for direct detection.

Solving the cosmic lithium problems with primordial late-decaying particles

We investigate the modifications to predictions for the abundances of light elements from standard big-bang nucleosynthesis when exotic late-decaying particles with lifetimes exceeding {approx}1 sec are prominent in the early Universe. Utilizing a model-independent analysis of the properties of these long-lived particles, we identify the parameter space associated with models that are consistent with all observational data and hence resolve the much discussed discrepancies between observations and theoretical predictions for the abundances of {sup 7}Li and {sup 6}Li.

Local dark matter clumps and the positron excess

It has been proposed that the excess in cosmic ray positrons at approximately 8 GeV, observed on both flights of the High-Energy Antimatter Telescope (HEAT) balloon experiment, may be associated with the annihilation of dark matter within the Milky Way halo. In this paper, we demonstrate how the self-annihilation of neutralino dark matter within local substructure can account for this excess, and we estimate the annihilation cross-section for several benchmark minimal supersymmetric (MSSM) models. We also demonstrate the changes in the permitted parameter space as the effects of tidal disruption become increasingly severe.

Signatures of clumpy dark matter in the global 21 cm background signal

We examine the extent to which the self-annihilation of supersymmetric neutralino dark matter, as well as light dark matter, influences the rate of heating, ionization, and Lyman-{alpha} pumping of interstellar hydrogen and helium and the extent to which this is manifested in the 21 cm global background signal. We fully consider the enhancements to the annihilation rate from dark matter halos and substructures within them. We find that the influence of such structures can result in significant changes in the differential brightness temperature, {delta}T{sub b}. The changes at redshifts z<25 are likely to be undetectable due to the presence of the astrophysical signal; however, in the most favorable cases, deviations in {delta}T{sub b}, relative to its value in the absence of self-annihilating dark matter, of up to {approx_equal}20 mK at z=30 can occur. Thus we conclude that, in order to exclude these models, experiments measuring the global 21 cm signal, such as EDGES and CORE, will need to reduce the systematics at 50 MHz to below 20 mK.

Accounting for the Unresolved X-ray Background with Sterile Neutrino Dark Matter

We consider a scenario where keV sterile neutrinos constitute all of the currently inferred dark matter abundance, whose radiative decays could potentially account for the flux contributions to the X‐ray background (XRB) by unresolved sources. Here we apply integrated flux methods to results from the observations of the North/South Chandra deep fields (CDF‐N/S) in order to deduce constraints on the sterile neutrino mass‐mixing parameters.