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[astro-ph/0508572] Observational Evidence for Extra Dimensions from Dark Matter
 
Authors:Bo Qin, Ue-Li Pen, Joseph Silk
Abstract:Recent astronomical observations of systems of dark matter, which have been cited as providing possible support for self-interacting cold dark matter, may provide evidence for the extra dimensions predicted by superstring scenarios. We find that the properties of the required dark matter self-interaction are precisely the consequences of a world with 3 large extra dimensions of size \~1nm, where gravity follows the r^{-5} law at scales below ~1nm. From the cross sections measured for various dark matter systems, we also constrain the mass of dark matter particles to be m_x ~ 3*10^{-16} proton mass, consistent with the mass of axions.
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Fergus Simpson



Joined: 25 Sep 2004
Posts: 27
Affiliation: University of Barcelona

PostPosted: August 31 2005  Reply with quote

This paper certainly makes some big claims! Would be interested to hear the thoughts of anyone working in this area....
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Simon DeDeo



Joined: 26 Oct 2004
Posts: 46
Affiliation: Santa Fe Institute

PostPosted: August 31 2005  Reply with quote

It is a fun paper to read (just skimming it now.) I am curious – how well established is the problem of "missing power"; one would imagine, for example, that baryons would act to smudge out what would otherwise be cuspy profiles on small scales without the need for an additional collisional component to the CDM self-interaction.

How well do we understand CDM+baryon systems? Any simulation gurus out there want to weigh in?
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Gil Holder



Joined: 25 Sep 2004
Posts: 27
Affiliation: McGill University

PostPosted: September 01 2005  Reply with quote

One of my colleagues here (Guy Moore) pointed out that the deBroglie wavelength is not only much bigger than the scattering length, as they point out, but is also much larger than the mean interparticle spacing. That would seem to indicate that treating this as one particle scattering off another is a bit simplistic, at best.

Roughly, the deBrogile wavelength should be order km, and the mean interparticle spacing must be of order sub-um near the galactic center. The effective graininess should be reduced by having of order 1030 particles per deBrogilie wavelength.

To quote Guy:
Quote:
this is the reason that light does not scatter appreciably in going
through a liquid or a glass;

this is why neutrinos and (perhaps) CDM particles can scatter coherently
from nuclei, rather than nucleon by nucleon;

it is why long wavelength phonons are ballistic in an amorphous medium,
but short wavelength phonons move diffusively.



Seems like a pretty good argument to me.
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