Dark Matter’s Daily Modulation

August 26, 2014

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Projected density plot of a redshift z=2.5 dark matter halo from a cosmological N-body simulation. The visible part of the galaxy (not shown in the image) lies at the dense centre of the halo and has a diameter of roughly 20 kiloparsecs. There are also many satellite galaxies, each with its own subhalo which is visible as a region of high dark matter density in the image. (c) WikiMedia

Deep underground a number of sophisticated experiments are seeking to detect the energy imparted to a nucleus from Dark Matter scattering. This Dark Matter comprises most of the mass of the Milky Way. If our understanding of Dark Matter is correct, then the Earth is bathed in a sea of Dark Matter which only occasionally bothers to interact with nuclei. When it does however, the energy it imparts to the nucleus in the scattering event can be detected experimentally. These experiments are usually buried deep underground so as to shield the detector from cosmic rays and other background processes that mimic DM scattering.

Typically it has been assumed that Dark Matter interacts so feebly with ordinary matter that it simply travels from outside the Earth to the detector unimpeded. Chris Kouvaris and Ian Shoemaker have recently posted a paper to the arXiv demonstrating that the interactions of Dark Matter and nuclei can slow or completely stop an incoming Dark Matter particle. In addition to altering experimental limits, this effect can be exploited to look for a daily modulation in the Dark Matter signal. This was recently discussed on Videnskab.