It would also lead to a
time dependence of the expansion contrary to observations,

In article ,
David Staup writes:
I thought we have seen a rate of expansion that is increasing over
time...no?

The observed change in expansion rate with time is consistent with a
cosmological constant, which I believe means that acceleration is
constant with time. The technical description is that parameter w
has a value very close to -1.

If I understand the original suggestion of dark matter particles that
repel each other, their average distance apart would increase with
time, and the simple expectation would be that the repulsive force
would change, giving w different from -1. One could presumably
overcome this by making the force-distance law just what is needed,
but I don't see how to overcome the other problems with the idea.

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