I don't think it's dark energy or dark matter at all.
I think the extra gravity attributed to "dark matter" is actually gravitational leakage from phase-shifted parallel universes that have branched off from our own universe.
Think of the movie "Sliding Doors" as an example. Every time a decision is made by any intelligent creature, it creates a multitude of alternate timelines which in effect are alternate universes that have branched off from our timeline/universe.
Depending on how many possible different options there were for each decision made is the determining factor for how many branching timeline universes are created by a decision event.
Since there are billions of decisions being made every second of every day by any creature with any intelligence at all, there must be untold trillions of universes constantly being created every second of every day.
If gravity is not bound by the vibrational phase shift that separates these universes, then gravity is constantly being increased by the number of universes branching off of ours, so the gravity from adjacent universes helps hold galaxies together in ours, and theirs.
Now as to "dark energy" and cosmic expansion, it's simple, really.
Every alternate universe created by a decision point also creates a duplicate of all the matter *and space-time* in this universe, effectively doubling the mass and volume of both matter and *space-time* for each time you choose to go left instead of right.
The universe is being forced to expand because of the massively exponential increase in the number of comoses being continuously duplicated off our branch.
We're continuously increasing the amount of space itself, so it must continuously expand.
That, and we're alive in *this* universe because it's the one that we didn't die in.