In article ,
David Staup writes:
Is it possible that Dark Matter is repulsive to itself (by whatever
mechanism) while being attracted (by gravity) to normal matter?

That would be inconsistent with general relativity, but that's no
reason not to consider the possibility. I don't see how repulsive
dark matter could clump up, though, as seems to be needed for galaxy
clusters and to explain CMB fluctuations. It would also lead to a
time dependence of the expansion contrary to observations, which are
consistent with a cosmological constant that does not vary in time.

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