The observed gravitational lensing in the areas adjacent to the merging galaxies is an interesting discovery, but there must be other theoretical explanations for it. I think Photoshop retouching, as seen in the image, can be somewhat misleading to the typical casual space enthusiast who could believe that sensors actually imaged dark matter. In a recent SDC article, gravity waves were discussed as a possible explanation for certain observations. I wonder if the same phenomenon could be used to explain what is occurring there.
There are other theoretical explanations for the Bullet Cluster observations, but if we believe in Occam's Razor, then it looks strikingly like dark matter. This is exactly what cold dark matter structure formation theories predicted before Bullet Cluster was observed.
As for this paper, it sounds interesting, but I can't find it after a quick look-through. It's possible (as happens often) the news release folks at Harvard are blowing up a speculative result from a paper otherwise about much more down-to-earth things.
Oh! I'm not sure why I didn't see that. It's possible I was looking for Finkbeiner as the first author (forgetting the high-energy physics authorship convention). Those are some serious scientists... no crackpots here (even though they're at Harvard!). I didn't see anything in the paper about cluster observations like the Bullet Cluster, though. As someone who knows a lot more about astronomy than about particle physics, that's one of the first things that comes to mind. Any new theory of dark matter has a lot of varied observations to explain. Despite having a moniker in common, dark matter and dark energy are nothing alike. Dark energy is invoked to explain one thing - the accelerated expansion of the universe. Alternate theories need to do one thing, and that is explain the acceleration while not contradicting known physics. Dark matter, on the other hand, can't be localized to any one event or phenomenon. There's a multitude of evidence, and a new theory has to reflect that.