I What is the difference between collisionless and self-interacting dark matter?

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Collisionless dark matter refers to particles that do not scatter or collide with each other, interacting primarily through gravity, as described by the Lambda Cold Dark Matter (LCDM) model. In contrast, self-interacting dark matter (SIDM) allows for interactions between dark matter particles, which can lead to different cosmic structures and dynamics. The discussion emphasizes the importance of understanding these distinctions to grasp dark matter's role in the universe. Clarifying these terms is crucial for advancing theories in cosmology. Overall, the differences between collisionless and self-interacting dark matter have significant implications for our understanding of the universe.
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When dark matter is called collisionless, does it only mean that they do not collide and scatter, or does it also mean that there is no other significant non-contact interaction?
 
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That would be the LCDM theory of dark matter.
I would think collisionless means no physical scattering, no interaction whatsoever, except through gravity.
But let us have a second opinion before you send off.
Keep you finger on the keyboard.

There is also the SIDM - self interacting dark matter.
 

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