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Published May 15, 2008 | Published
Journal Article Open

Galactic substructure and direct detection of dark matter


We study the effects of substructure in the Galactic halo on direct detection of dark matter, on searches for energetic neutrinos from weakly interacting massive particles (WIMP) annihilation in the Sun and Earth, and on the enhancement in the WIMP annihilation rate in the halo. Our central result is a probability distribution function (PDF) P(rho) for the local dark-matter density. This distribution must be taken into account when using null dark-matter searches to constrain the properties of dark-matter candidates. We take two approaches to calculating the PDF. The first is an analytic model that capitalizes on the scale-invariant nature of the structure-formation hierarchy in order to address early stages in the hierarchy (very small scales; high densities). Our second approach uses simulation-inspired results to describe the PDF that arises from lower-density larger-scale substructures which formed in more recent stages in the merger hierarchy. The distributions are skew positive, and they peak at densities lower than the mean density. The local dark-matter density may be as small as 1/10th the canonical value of ~=0.4 GeV cm^-3, but it is probably no less than 0.2 GeV cm^-3.

Additional Information

© 2008 The American Physical Society. (Received 22 January 2008; revised 22 March 2008; published 13 May 2008) We acknowledge useful conversations with A. Benson, S. Habib, K. Heitmann, G. Jungman, D. Nagai, and D. Reed. SMK thanks Caltech for hospitality while this work was being conceived. Work at LANL was carried out under the auspices of the NNSA of the U.S. Department of Energy at Los Alamos National Laboratory under Contract No. DE-AV52-06NA25396. This work was supported at Caltech by DoE DE-FG03-92-ER40701, NASA NNG05GF69G, and the Gordon and Betty Moore Foundation.

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