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Dark matter equation of state
 
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Dario Bettoni



Joined: 13 Jan 2010
Posts: 1
Affiliation: Technion

PostPosted: December 02 2011  Reply with quote

For work purposes I was looking around trying to understand which constraint we have from observations to the equation of state of the dark matter. It turns out that we don't know that much. If from CMB, SNIa nad LSS we can constraint w=0 with high precision, not the same accuracy on small scales.

Does anybody know some reference on this topic?

I just have a couple:

[1] A. L. Serra and M. J. L. D. Romero, Monthly Notices of the Royal Astronomical Society: Letters 415, L74–L77 (2011).
[2] C. Müller, Phys. Rev. D 71, (2005)

Thanks,

Dario Bettoni
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Maciej Bilicki



Joined: 12 May 2010
Posts: 19
Affiliation: University of Cape Town

PostPosted: December 02 2011  Reply with quote

What do you mean by equation of state? On largest scales dark matter and baryons are dust with w=0. On small scales baryons are no longer dust (e.g. could be ideal gas with p dependent not only on ρ) but for DM I think we would first need to understand what it is made of to speak of some specific equation of state. Still, as it doesn't interact electromagnetically, I can hardly imagine associating some pressure to it? Perhaps I'm wrong.
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Ben Gold



Joined: 25 Sep 2004
Posts: 97
Affiliation: University of Minnesota

PostPosted: December 07 2011  Reply with quote

Calabrese et al. (PRD 80, 063539, 2009) seems to be the sort of thing you're looking for. For some reason it's not on the arXiv, though. The NASA ADS link is: http://adsabs.harvard.edu/abs/2009PhRvD..80f3539C

I'm pretty sure the basic answer is that if you believe WMAP and H0 measurements, then you really can't have very much dark matter that's warm, for much the same reasons you get limits on the total mass in neutrinos. WDM streaming out of potential wells would mess up the power spectrum on small scales in a rather noticable way (especially now with ACT and SPT, I'm not sure the H0 prior is still even necessary).
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Simon DeDeo



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

PostPosted: December 07 2011  Reply with quote

In addition to the WDM question (and related constraints coming from neutrino masses), unusual equations of state (and, correspondingly, unusual sound speeds) are a long-running topic – http://background.uchicago.edu/~whu/Papers/gdm.pdf is a classic reference. DM cross-sections (related to w and cs questions) became a question empirically with the discovery of the bullet cluster (and related objects.) I would be surprised if CAMB these days did not allow you to try a range of w(z) and cs(z) curves.
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