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[astro-ph/0610336] How well can (renormalized) perturbation

Posted: October 15 2006
by Anze Slosar
This is quite an interesting paper that attempts to find the fundemental limit that any perturbative scheme could, in principle, achieve. I think that the idea of using sticky DM model is quite clever, but I am not sure about the execution. The halo model as a paradigm is based on standard N-body stuff, so to a certain extent you get out what you put in: it is to be expected that the two models will start to diverge when the 1-halo term kicks; in other words the result of this paper puts a lower limit on where the two cases would actually diverge... So, to do it properly, one would need to run an N-body with sticky particles (I think that something similar has already been done to treat star-formation - not sure if that stickiness is of the right sort)

Besides, how does this relate to the work done in astro-ph/0605012? I vaguelly remember talking to Peter Coles, who claimed that his approach survives shell-crossing (but I can't be asked to read 45 pages on Sunday :) )

[astro-ph/0610336] How well can (renormalized) perturbation

Posted: October 15 2006
by Niayesh Afshordi
Anze, Thanks for your comment.

Doing a simulation of sticky DM was the first thing that came to my mind, but was not sure that it was worth the effort.

After I posted the preprint, Roya Mohayee reminded me that sticky DM is in fact very similar to the adhesion model, which is a way to continue Zeldovich approximation beyond shell crossing. Adhesion model is simply adding a tiny viscosity to the Euler equation to regularize caustics, without heating up the fluid. So I think it must be fairly easy to simulate.

However, I'm still not sure if it is worth doing a simulation in order to get an estimate of the error lower limit. As I say in the paper, on larger scales, the difference btw sticky and collisionless DM is dominated by the 2-halo term, which gives a rough estimate of the error if you screw things up in the virialized regions.