Editing Weakly interacting massive particle (section)

== As dark matter ==

A decade after the dark matter problem was established in the 1970s, WIMPs were suggested as a potential solution to the issue.<ref>{{cite journal|last1=de Swart|first1=J. G.|last2=Bertone|first2=G.|last3=van Dongen|first3=J.|title=How dark matter came to matter|journal=Nature Astronomy|date=2017|volume=1|issue=59|pages=0059|doi=10.1038/s41550-017-0059|arxiv = 1703.00013 |bibcode = 2017NatAs...1E..59D |s2cid=119092226}}</ref> Although the existence of WIMPs in nature is still hypothetical, it would resolve a number of astrophysical and cosmological problems related to dark matter. There is consensus today among astronomers that most of the mass in the Universe is indeed dark. Simulations of a universe full of cold dark matter produce galaxy distributions that are roughly similar to what is observed.<ref>{{cite journal |arxiv=astro-ph/0512234 |last1=Conroy |first1=Charlie |title=Modeling Luminosity-Dependent Galaxy Clustering Through Cosmic Time |journal=The Astrophysical Journal |volume=647 |issue=1 |pages=201–214 |last2=Wechsler |first2=Risa H. |last3=Kravtsov |first3=Andrey V. |year=2006 |doi=10.1086/503602|bibcode=2006ApJ...647..201C |s2cid=13189513 }}</ref><ref>The Millennium Simulation Project, [http://www.mpa-garching.mpg.de/galform/virgo/millennium/ Introduction: The Millennium Simulation] The Millennium Run used more than 10 billion particles to trace the evolution of the matter distribution in a cubic region of the Universe over 2 billion light-years on a side.</ref> By contrast, [[hot dark matter]] would smear out the large-scale structure of galaxies and thus is not considered a viable cosmological model.

WIMPs fit the model of a relic dark matter particle from the early Universe, when all particles were in a state of [[thermal equilibrium]]. For sufficiently high temperatures, such as those existing in the early Universe, the dark matter particle and its antiparticle would have been both forming from and annihilating into lighter particles. As the Universe expanded and cooled, the average thermal energy of these lighter particles decreased and eventually became insufficient to form a dark matter particle-antiparticle pair. The annihilation of the dark matter particle-antiparticle pairs, however, would have continued, and the number density of dark matter particles would have begun to decrease exponentially.<ref name="Kamionkowski" /> Eventually, however, the number density would become so low that the dark matter particle and antiparticle interaction would cease, and the number of dark matter particles would remain (roughly) constant as the Universe continued to expand.<ref name="Griest" /> Particles with a larger interaction cross section would continue to annihilate for a longer period of time, and thus would have a smaller number density when the annihilation interaction ceases. Based on the current estimated abundance of dark matter in the Universe, if the dark matter particle is such a relic particle, the interaction cross section governing the particle-antiparticle annihilation can be no larger than the cross section for the weak interaction.<ref name="Kamionkowski" /> If this model is correct, the dark matter particle would have the properties of the WIMP.