With such long wavelengths they wouldn’t interact much if at all with matter, but if there were enough of them (produced in the Big Bang shortly after the Universe dropped below the elecroweak unification temperature?) they would exert a significant gravitational force.

(It may be the Bullet cluster is enough to put paid to this idea, if dark matter remains localized after being bumped aside from its host galaxy.)

Isn’t it better to think of stars collecting in pools of dark matter?

Or really, since they both influence and follow spacetime curvature, DM and ordinary matter ought to collect into wells together, with more massive objects tending to sift (or at least be found) “downward” eventually.

Are there degenerate phases of dark matter? How much denser is DM near the centre of large scale structures than in galactic halos or in inter-galactic space?

I had precisely the same reaction as Valerie about your comment that arXiv publication is what matters. All of us who write about science these days do write stories based on what comes from the arXiv but we all receive negative comments from scientists for doing it. It doesn’t stop us from doing it! However, having something to peg the story to, like journal publication, helps us choose what stories to cover among the many possible options, especially if we didn’t catch it first time around.

I also agree that the Physics piece could have done with some more context about the Nature paper. Apparently Physics takes letters to the editor although I don’t think I’ve seen any yet. Perhaps it would be worth something brief…

I still think it was worth pointing out this paper now, especially given that, as you pointed out, it hadn’t had any coverage previously but is an important part of the story. Cosmic Variance had talked about the positron paper but not the anti-proton paper, for example. I see that PhysicsWorld has just done a piece on this paper as well: http://physicsworld.com/cws/article/news/37665

It might not be new, but it still seems to be news.

Sean: Nope, I meant “find a fudge factor” – it is astrophysics afterall.

Scientists could legitimately be annoyed if a crazy paper that never would have passed peer review were picked from the arxiv and widely publicized. But if a paper is sensible, I personally don’t see what difference it makes that it’s been peer-reviewed or not. The idea that a result doesn’t really “exist” until it appears in a peer-reviewed journal is a fiction that is becoming increasingly difficult to maintain.

Of course, I am a theorist, and most of my experience is with theoretical papers. Experimentalists might feel differently, and are welcome to chime in.

Also, physicists just like to berate people, so don’t take it personally.