Can Heavy WIMPs Be Captured by the Earth?

TL;DR

This paper questions whether heavy WIMPs can be captured by the Earth if solar-system resonances deplete bound WIMPs by driving them into the Sun. It reviews the traditional capture framework, then presents two developments that could alter capture: rapid Sun-driven depletion of bound WIMPs (inspired by asteroid dynamics) and the Damour–Krauss mechanism that could temporarily boost low-velocity WIMPs. Using ultra-conservative and Jupiter-repopulation scenarios, the authors show that Earth capture—and thus neutrino-based limits—become strongly suppressed for $M_x \gtrsim 150\ \mathrm{GeV}$ and vanish for $M_x \gtrsim 630\ \mathrm{GeV}$, meaning current non-detections do not constrain the heaviest WIMPs. The work highlights the need for detailed orbital simulations of WIMPs to determine whether standard Gould limits can be applied, since the solar-system dynamics could dramatically alter the interpretation of neutrino searches.

Abstract

If weakly interacting massive particles (WIMPs) in bound solar orbits are systematically driven into the Sun by solar-system resonances (as Farinella et al. have shown is the case for many Earth-crossing asteroids), then the capture of high-mass WIMPs by the Earth would be affected dramatically because high-mass WIMPs are captured primarily from bound orbits. WIMP capture would be eliminated for M_x>630 GeV and would be highly suppressed for M_x>~150 GeV. Annihilation of captured WIMPs and anti-WIMPs is expected to give rise to neutrinos coming from the Earth's center. The absence of such a neutrino signal has been used to place limits on WIMP parameters. At present, one does not know if typical WIMP orbits are in fact affected by these resonances. Until this question is investigated and resolved, one must (conservatively) assume that they are. Hence, limits on high-mass WIMP parameters are significantly weaker than previously believed.

Figures (1)

• Figure 1: Conservative capture rates for WIMPs relative to the rate based on the naive assumption (Gould 1991) that the phase-space density of WIMPs bound to the Sun is similar to that of low-velocity unbound WIMPs. The solid curve shows the suppression factor under the ultra-conservative assumption that all bound WIMPs are driven into the Sun on short time scales (as is true of many Earth-crossing asteroids). The bold curve results from the more realistic assumption that WIMPs on Jupiter-crossing (and Earth-crossing) orbits are repopulated faster than they can be driven into the Sun.