* Astronomy

Title: Dark matter in the solar system I: The distribution function of WIMPs at the Earth from solar capture
Authors: Annika H. G. Peter

The next generation of dark matter (DM) direct detection experiments and neutrino telescopes will probe large swaths of dark matter parameter space. In order to interpret the signals in these experiments, it is necessary to have good models of both the halo DM streaming through the solar system and the population of DM bound to the solar system. In this paper, the first in a series of three on DM in the solar system, we present simulations of orbits of DM bound to the solar system by solar capture in a toy solar system consisting of only the Sun and Jupiter, assuming that DM consists of a single species of weakly interacting massive particle (WIMP). We describe how the size of the bound WIMP population depends on the WIMP mass, spin-independent cross section, and spin-dependent cross section. Using a standard description of the Galactic DM halo, we find that the maximum enhancement to the direct detection event rate, consistent with current experimental constraints on the WIMP-nucleon cross section, is < 1% relative to the event rate from halo WIMPs, while the event rate from neutrinos from WIMP annihilation in the center of the Earth is unlikely to meet the threshold of next-generation, km³-sized (IceCube, KM3NeT) neutrino telescopes.

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Title: Dark Matter
Authors: Jaan Einasto

A review of the development of the concept of dark matter is given. I begin the review with the description of the discovery of the mass paradox in our Galaxy and in clusters of galaxies. In mid 1970s the amount of observational data was sufficient to suggest the presence of a massive and invisible population around galaxies and in clusters of galaxies. The nature of the dark population was not clear at that time, but the hypotheses of stellar as well as of gaseous nature of the new population had serious difficulties. These difficulties disappeared when non-baryonic nature of dark matter was suggested in early 1980s. In addition to the presence of Dark Matter, recent observations suggest the presence of Dark Energy, which together with Dark Matter and ordinary baryonic matter makes the total matter/energy density of the Universe equal to the critical cosmological density. There are various hypothesis as for the nature of the dark matter particles, and generally some form of weakly interactive massive particles (WIMPs) are strongly favoured. Both Dark Matter and Dark Energy are the greatest challenges for modern physics since their nature is unknown.

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New detector will aid dark matter search
Several research projects are underway to try to detect particles that may make up the mysterious "dark matter" believed to dominate the universe's mass. But the existing detectors have a problem: They also pick up particles of ordinary matter -- hurtling neutrons that masquerade as the elusive dark-matter particles the instruments are designed to find.
MIT physicist Jocelyn Monroe has a solution. A new detector she and her students have built just finished its initial testing last week at Los Alamos National Laboratory. When deployed in the next few months alongside one of the existing dark-matter detectors, the new device should identify all of the ordinary neutrons that come along, leaving anything else that the other detector picks up as a strong candidate for the elusive dark matter.

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Universe's dark matter mix is 'just right' for life
It's not just the nature of dark matter that's a mystery - even its abundance is inexplicable. But if our universe is just one of many possible universes, at least this conundrum can be explained.
The total amount of dark matter - the unseen stuff thought to make up most of the mass of the universe - is five to six times that of normal matter. This difference sounds pretty significant, but it could have been much greater, because the two types of matter probably formed via radically different processes shortly after the big bang. The fact that the ratio is so conducive to a life-bearing universe "looks like a tremendous coincidence", says Raphael Bousso at the University of California, Berkeley.

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