# Is Dark Matter a superfluid

1. Jul 14, 2015

### wolram

This the best description of Dark Matter i have come across, it uses the LCDM and MOND to create a best fit model.

arXiv:1507.03013 [pdf, other]
A Dark Matter Superfluid
Justin Khoury
Comments: 8 pages. To appear in the proceedings of the 2015 Rencontres de Moriond, "Gravitation: 100 years after GR"
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Other Condensed Matter (cond-mat.other); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)

In this talk we present a novel framework that unifies the stunning success of MOND on galactic scales with the triumph of the LambdaCDM model on cosmological scales. This is achieved through the rich and well-studied physics of superfluidity. The dark matter and MOND components have a common origin, representing different phases of a single underlying substance. In galaxies, dark matter thermalizes and condenses to form a superfluid phase. The superfluid phonons couple to baryonic matter particles and mediate a MOND-like force. Our framework naturally distinguishes between galaxies (where MOND is successful) and galaxy clusters (where MOND is not): dark matter has a higher temperature in clusters, and hence is in a mixture of superfluid and normal phase. The rich and well-studied physics of superfluidity leads to a number of striking observational signatures, which we briefly discuss. Remarkably the critical temperature and equation of state of the dark matter superfluid are similar to those of known cold atom systems. Identifying a precise cold atom analogue would give important insights on the microphysical interactions underlying DM superfluidity. Tantalizingly, it might open the possibility of simulating the properties and dynamics of galaxies in laboratory experiments.

What do you think, will they find these cold atoms?

Last edited: Jul 14, 2015
2. Jul 14, 2015

### Chalnoth

I am not encouraged by their use of a "stars and gas" rotation curve as if it were a $\Lambda$CDM rotation curve. Looks like they're comparing a model with no dark matter at all to MOND, which is stacking the deck.

Could be an interesting idea, but their decision to lie with graphs is more than a little troubling.

3. Jul 14, 2015

### wolram

Thanks Garth, i new their fits were to good to be true, however i find the idea of super fluidity interesting.

4. Jul 14, 2015

### marcus

I did not see any evidence of a deliberate decision to lie.
the author is Justin Khoury (solo)
He simply made a typo AFAICS and said "(blue)" where he meant to say "(red)". He says he copied the illustration from a 2009 Milgrom paper and if you look at that paper it is clear that the LambdaCDM case is the RED curve.

Chalnoth, this is a preprint. Justin simply made an error in referring to the color. the labeling on Milgrom's graph still makes it obvious. That is the kind of trivial error that gets corrected in version 2 or anyway before publication. IMHO it hardly seems a determined bare-faced lie (which anybody could catch by comparing with the original.)

Here's Milgrom's 2009 caption on the identical figure:
==quote==
Fig. 3.— The measured rotation curve of the galaxy NGC1560 shown by the data points. The predicted Newtonian curve based on the measured mass distribution is shown in blue. It shows a velocity disparity of a factor 2.25 at the last measured point, which corresponds to a factor-of-five mass discrepancy. The MOND prediction is shown in green. The best fit with a dark matter hallo of the type predicted by CDM simulations is shown in red.
==endquote==

5. Jul 14, 2015

### marcus

Wooly, that comment was by Chalnoth, not Garth. One isolated typo in the caption of an otherwise clearly labeled figure does not discredit a paper. the author is Justin Khoury. A reputable guy.
http://inspirehep.net/author/profile/J.Khoury.1 Young, but already has an average of 90 citations per published paper. I think he was born around 1978 which put him in his 30s.

I think he has an interesting idea. His fits are not too good to be true. It is common knowledge that MOND does very well at galactic scale and the fits he shows are similar to what many other people have shown. He is proposing a way that DM could DUPLICATE the good performance of MOND at that scale and explaining how it would behave more like what we expect of DM at larger scale where the DM still has a lot of random kinetic energy and hasn't condensed.

It is too early to shoot that idea down or reject it out of hand. I think other researchers will be interested and want to explore it.

Last edited: Jul 14, 2015
6. Jul 15, 2015

### Chalnoth

Ahh, my mistake. I guess it isn't nearly as bad as I thought.

But I still think the paper would have been better-off without that graph entirely because even interpreted correctly it's misleading: it's one of a huge number of galaxies whose rotation curves have been measured, and there's a high probability that the dark matter halo model used in that particular galaxy is incorrect (Much of the time the over-simplified NFW profile is used, which is known to not be all that accurate for relaxed galaxies, and is far worse for galaxies that have undergone recent mergers).

7. Jul 15, 2015

### wolram

My apologies to Chalnoth
Marcus i flagged up this paper because it is the only fit for dark matter that i have seen and i like the idea of super fluidity , you know i am skeptical but i am willing to be persuaded.

Last edited: Jul 15, 2015
8. Jul 15, 2015

### Chalnoth

Incidentally, I'm not sure it's accurate to say that MOND works well at galactic scales, given that there seem to be large discrepancies in gravitational lensing:
http://arxiv.org/abs/1205.4880

9. Jul 15, 2015

### marcus

Wooly, I'm glad you flagged this one. It is an interesting new idea.

It is too early to try to guess if it is right or wrong. It is too new for that. the question is whether you find it interesting and worth seriously considering, or whether you reject it out of hand.

http://arxiv.org/abs/1507.03013

the key idea is that DM can undergo a PHASE CHANGE so that there are two different ways it can act (like water can be a gas or it can condense to a liquid)

the idea is that DM can have something like a "temperature" which measures the amount of random motion of its particles. In a cluster of galaxies the individual motion of particles is chaotic and incoherent, too much random kinetic energy, preventing them from condensing.
so DM acts like we have always imagined, as a kind of gas that contributes to the mass holding the cluster together.

but in a galaxy the DM has had a chance to have its motions smoothed out and "cooled" so it flows in a more coherent way (according to this idea) and even though it only interacts with ordinary matter OM via gravity it can influence the OM and maybe "sweep it along" to a slight extent.
Maybe the DM can develop density waves, undulations of arms of higher density separated by gaps of lower density, and stuff like that.

Anyway the temperature of the DM can influence how it acts, and (according to this idea) improve the fit.

For example where two galaxies have collided you can imagine that the DM coherence is disrupted and its motions are more chaotic so it would change phase back to the "higher temperature " form. But undisturbed in a spiral galaxy it would settle down into the more coherent lower temperature form. So then it would produce the somewhat improved "MOND-like" fit to the data.

I think I will not try to discuss this further and out-guess the experts. As a non-expert interested observer I will simply wait to see if Justin Khoury gets invited to other high profile prestigious conferences to present his idea. (He already presented it at Moriond, which is an elite venue) and I will wait to see if other authors CITE this paper. this link will give the citations:
http://inspirehep.net/record/1382539?ln=en