Inastrophysics andparticle physics,self-interacting dark matter (SIDM) is an alternative class ofdark matter particles that have strong interactions, in contrast to the standardcold dark matter model (CDM). SIDM was postulated in 2000^[1] as a solution to thecore-cusp problem.^[2][3][4] In the simplest models of DM self-interactions, a Yukawa-type potential and a force carrierφ mediates between two dark matter particles.^[5] On galactic scales, DM self-interaction leads to energy and momentum exchange between DM particles. Over cosmological time scales this results in isothermal cores in the central region of dark matter haloes.

If the self-interacting dark matter is inhydrostatic equilibrium, its pressure and density follow:

${\displaystyle \mathrm{\nabla }{P}_{\chi }/{\rho }_{\chi }=\mathrm{\nabla }{\mathrm{\Phi }}_{\text{tot}}=\mathrm{\nabla }({\mathrm{\Phi }}_{\chi }+{\mathrm{\Phi }}_{\text{b}}),}$

where${\displaystyle {\mathrm{\Phi }}_{\chi }}$ and${\displaystyle {\mathrm{\Phi }}_{\text{b}}}$ are the gravitational potential of the dark matter and a baryon respectively. The equation naturally correlates the dark matter distribution to that of the baryonic matter distribution. With this correlation, the self-interacting dark matter can explain phenomena such as theTully–Fisher relation.

Self-interacting dark matter has also been postulated as an explanation for theDAMA annual modulation signal.^[6][7][8] Moreover, it is shown that it can serve the seed ofsupermassive black holes at high redshift.^[9] SIDM may have originated in a so-called "Dark Big Bang".^[10]

In July 2024 a study proposed SIDM solves the "final-parsec problem",^[11][12] two months later another study proposed the same withfuzzy cold dark matter.^[13][14]

• MACS J0025.4-1222, astronomical observations that constrain DM self-interaction
• ESO 146-5, the core ofAbell 3827 that was claimed as the first evidence of SIDM
• Strongly interacting massive particle (SIMP), proposed to explain cosmic ray data
• Lambda-CDM model

• Bertone, Gianfranco (2010).Particle Dark Matter: Observations, Models and Searches.Cambridge University Press. p. 762.Bibcode:2010pdmo.book.....B.ISBN 978-0-521-76368-4.
• Musser, George (May 2000)."What's the Matter?".Scientific American.282 (5): 24.Bibcode:2000SciAm.282e..24M.doi:10.1038/scientificamerican0500-24.
• Lawrence, Krauss (2000).Quintessence: The Search for Missing Mass in the Universe.Basic Books. p. 384.ISBN 978-0-465-03741-4.

• Astroparticle physics
• Dark matter

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