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The Net Advance of Physics: The Nature of Dark Matter, by Kim Griest -- Section 7J.

Next: Acknowledgements Up: Machos Previous: Macho Conclusion


The dark matter situation has changed dramatically in the past few

years. Not long ago, people agreed that the dark matter existed, but

had little hope of knowing what it actually consisted of. Now strong

detection efforts are underway for many of the best candidates. For

Machos, first results are already in, and it seems quite probable that

the bulk of the dark matter does not consist of Machos in the Earth

to brown dwarf mass range. There is still a ``baryonic dark matter"

window for exotic objects in the solar to 1000 solar mass range.

Turning to Wimps, we found that these are excellent dark matter

candidates for a variety of reasons, and that three methods of

detection are being vigorously pursued: high energy accelerators,

direct detection, and via high energy neutrinos from the Sun.

Axions also are fine dark matter candidates, and the new

microwave cavity experiments will for the first time probe some of

the best axion parameter space. However, no experiments capable

of definitively ruling out either axion or Wimp candidates are

underway, so there is the chance that either could be the dark

matter without us discovering it.

No one has yet found a method to directly detect a light neutrino

component of the dark matter, though interest in these as

candidates for the ``hot dark matter" component in a mixed hot

plus cold dark matter galaxy formation scenario is very high. For

neutrinos, the most promising method is to measure the masses via

neutrino oscillation experiments, and then calculate the relic

density using the big bang theory. Indirect and preliminary evidence

for such neutrino oscillations already exists, so experiments capable

of actually determining neutrino masses should be watched with

great interest by all astrophysicists.

In conclusion, this is a very active field, and, remarkably, there is a

reasonable chance of discovering the nature of the dark matter

within the next few years.

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Next: Acknowledgements Up: Machos Previous: Macho Conclusion