Dark matter

mheslep

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I'm optimistic about the sterile neutrino, and could also explain baryon asymmetry and neutrino oscillations - which is interesting. It also looks like a natural extension to the standard model that does not require a massive paradigm shift. I anticipate a flood of papers on this over the next year or two. It might even influence the next cycle of LHC research, as these energy ranges are well within LHC capabilities. This could prove an enormous boon to the legacy of LHC and future research initiatives. We live in exciting times.
If true, then the majority of the mass in the universe consists 7 keV neutrinos? Would we not expect to find this to be the case in some celestial body with which we have long, common experience?
 

marcus

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If true, then the majority of the mass in the universe consists 7 keV neutrinos? Would we not expect to find this to be the case in some celestial body with which we have long, common experience?
Hi! That's a natural question, if there are these particles why haven't they collected and condensed in orbs like the sun? The answer is interesting.

Being able to radiate excess energy off into space actually helps clouds of stuff condense into more compact orbs.

If something can't interact with the EM field it can't radiate!

Particles can be attracted by a massive body and zoom in but they have no way to lose their kinetic energy so they just zoom on out again. To condense you have to be able to DUMP excess gravitational potential energy so you can settle down into something more compact.

So the question is, *how do you even get CLOUDS?* why isn't DM still as uniformly distributed as in early universe (e.g. as uniform as the CMB)?

That's interesting. I should really let Chronos answer since this is a current interest of his. It has to do with the SLINGSHOT EFFECT coupled with metric EXPANSION.
If particles can interact gravitationally they can transfer energy and some lose KE and settle in while others gain KE and get flung OUT of the cloud. So the cloud can slowly contract while those exiles carrying away excess energy go on a long journey in expanding geometry.

But expansion saps the KE out of stuff. This is subtle. (I understand it's covered in Steven Weinberg's Cosmology text.) When the wanderer catches up to another cloud he may arrive with a speed closer to its average velocity and get trapped. It is analogous to redshift with light which reduces the momentum of the photons. The momentum of other particles (eg. neutrinos) is reduced by expansion as well. It is a beautiful process, anybody should ask about it if it puzzles them.

The bleeding off of excess energy by gravitational interaction coupled with metric expansion is slower and less efficient than what happens with ordinary matter (colliding, heating, radiating). But it is nevertheless effective enough to allow clouds of DM to form around galaxies and in clusters of galaxies.

Still DM remains less localized than ordinary matter.

And I should be mindful that we don't know what species of matter constitute DM. It might consist all or in part of these conjectured 7 keV sterile righthand neutrinos---a type of neutrino that seems to be missing from the standard particle model pattern. Or this recent observation by Maxim Markevitch and friends could be wrong and the 3.5 keV bump might not even be there, or have some other explanation. we all realize this but it doesn't hurt to be reminded.
 
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Chronos

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We live in exciting times.
 
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http://arxiv.org/abs/1402.5837

"The recently discovered X-ray line at about 3.5keV can be explained by sterile neutrino dark matter with mass, ms≃7keV, and the mixing, sin22θ∼10−10. Such sterile neutrino is more long-lived than estimated based on the seesaw formula, which strongly suggests an extra flavor structure in the seesaw sector. We show that one can explain both the small mass and the longevity based on the split flavor mechanism where the breaking of flavor symmetry is tied to the breaking of the B−L symmetry. In a supersymmetric case we find that the 7keV sterile neutrino implies the gravitino mass about 100TeV."


...They're really on to something specially on neutrino oscillation where it flips to such flavors mainly moun type in parity to mass splitting which has the potential to solve the mass problem.
 

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