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.