Cold Dark Matter as Compact Composite Objects

Composite Dark Matter with Invisible Light from Almost-Commutative Geometry

Spin half fermions with mass dimension one: theory, phenomenology, and dark matte

Generalized mirror matter models

Has DAMA Detected Self-Interacting Dark Matter?

http://arxiv.org/abs/astro-ph/0205464

It might turn out that none of them is serious, and messy astrophysics can fix them all — or not.

Can someone(Sean, Risa, Mark) summarize briefly as to what is the motivation for adding
these exotic properties to cold dark matter particles.

It’s all explained in this paper

Can someone(Sean, Risa, Mark) summarize briefly as to what is the motivation for adding
these exotic properties to cold dark matter particles. Is it to address the cold dark matter crisis
at smaller scales(which I thought from one of the ary posts on this blog) is not as severe as thought before?
Of course there are tons of candidates even for vanialla cold dark matter, though the WIMP
and axion are the most popular ones.

http://arxiv.org/abs/astro-ph/0602186

Basically, they are arguing that all of the Milky Way dwarf spheroidals have masses ~ 4 x 10^7 M_sun. The masses come from a straightforward application of the Jeans theorem, with the usual (and perhaps unjustified) assumptions like isotropy. Much of the conclusion is based upon velocity dispersion measurements in the outer parts of the galaxies from small numbers of stars.

The basic point seems to be that the DM is less concentrated — more spread out — in these galaxies than you might have thought it should be. There are other indications that dark matter doesn’t clump that effectively on small scales (a lack of cusps at the center of galaxies, a lack of small satellite galaxies), but those are messy because ordinary matter is also playing a role. If it’s true that these systems have much more DM than ordinary matter, it might make them a useful testing ground for these questions.

Mannheim in a 1999 paper addresses the original 1993 Knox and Kosowsky issue with nucleosynthesis. Yes, it appears to be a problem, but not necessarily unresolvable.

If this is the case, then one immediate objection is that you only measure the coarse-grained density, which is NOT conserved, but gives a lower bound on the (conserved) fine-grained density.

Also I believe that in simulated DM halos, the regions of high phase-space density are in the subhalos — the central core of a halo generally has pretty low phase-space density. Of course, you don’t probe the subhalos because they have no stars in them. So any estimate of the phase-space density based on the central stellar velocity dispersion is again bound to biased low. I don’t see how they can get anything besides an upper bound on the DM temperature.

Of course, they might have done something entirely different than what I’m guessing, I suppose we’ll have to wait for the paper to come out…

Are you sure this is the right blog?…

“On next: Most of Our Universe Is Missing
The world’s leading cosmologists seek the Universe’s most elusive secret.”

I have been waiting for this episode, so hopefully I will shed some light (pun intentional!) sometime tomorrow.

However, if you calculate the mass by assuming a velocity dispersion of 100 km/s (not sure if that’s correct for the galaxies they’ve looked at), you find that the mass is about 15 electron masses. That seems to be consistent with MeV Dark Matter

Dark matter doesn’t interact electromagnetically, so it won’t radiate electromagnetically. Possibly we don’t know enough to rule out other kinds of radiation, but I am guessing that if it does radiate at all then it isn’t in any currently detectable manner.

On a more general note, it seems that talking about warm and cold dark matter isn’t very helpful. The labels cold, warm and hot dark matter aren’t giving us enough distinction. I’ve already heard this stuff referred to as ‘lukewarm’ and ‘tepid’ in conversation.