I No Axions or Wimps

1. Oct 5, 2015

wolram

http://arxiv.org/pdf/1510.00400.pdf

Axions probably do not exist for theoretical reasons [19–21] discovered in 1992. Electroweak supersymmetry probably does not exist for the experimental reason [25–27] of its non-discovery in Run 1 of the LHC. The idea that dark matter experiences weak interactions (WIMPs) came historically from the appearance of an appealing DM constituent, the neutralino, in the theory of electroweak supersymmetry for which there is no experimental evidence.

So what is the possibility that Dark Matter is PBHs

2. Oct 5, 2015

wolram

search for WIMPS https://www.astro.umd.edu/~ssm/darkmatter/WIMPexperiments.html

Indeed, the experiments have perhaps been too successful. The original region of cross section-mass parameter space in which WIMPs were expected to reside was excluded years ago. Not easily dissuaded, theorists waved their hands, invoked the Majorana see-saw mechanism, and reduced the interaction probability to safely non-detectable levels. This is the vertical separation of the reddish and blue-green regions in the figure

3. Oct 5, 2015

Chalnoth

From everything I saw from the supersymmetry theorists, there remains a pretty large parameter space available for supersymmetry, and dark matter detection experiments are still just barely scratching the surface of the available parameter space for WIMPs.

As for primordial black holes, I believe the primary expected observational signal of those is seeing black hole decay: PBH's can be produced at any mass, so you'd expect a large number of very low-mass black holes, many of which would evaporate. Toward the end of a black hole's life, they get very hot. For example, when the black hole has about a year remaining, its temperature reaches into the petakelvin range ($10^{15}K$). Because it's so small, it's not terribly bright, but in the last few nanoseconds it becomes brighter than our Sun. This would produce a pretty distinctive signature of high-energy radiation.

4. Oct 5, 2015

Chalnoth

Also, let me add that high energy theorists were telling me from the start that the LHC would almost certainly not be able to detect the dark matter particle. There's a chance, so obviously experimentalists are trying, but the instrument just isn't designed for that.

5. Oct 5, 2015

wolram

It seems there is a little wiggle room for PBHs
http://arxiv.org/pdf/1307.4898v1.pdf

The cosmological constraints on PBHs have been reviewed by Carr et al [5]. The best method for constraining low mass PBHs (MBH ≤ 5 × 1014 g) is thus through their γ- ray emission. Previous searches have attempted to detect a diffuse photon signal from a distribution of PBHs [6] or to search directly for the final stage emission of an individual hole [9, 7, 8, 10]. The EGRET observation of the diffuse γ-ray background allowed to set an upper limit on the low mass PBH density ΩPBH of 0.2×10−9 to 2.6×10−9 [6]. The search for direct PBH explosions through γ-ray bursts did not find any evidence of their presence yet. The current upper limits on the local PBH explosion rate lie in the 105 - 106 pc−3 yr−1 range [5]. Note however that it has been argued that a class of very short gammay ray bursts are actually the final stage of PBH evaporation[11].

6. Oct 5, 2015

wolram

I found this paper that supports gamma ray busts originate from PBHs

http://arxiv.org/abs/1105.5363

We present the state of current research of Very Short Gamma Ray Bursts (VSGRBs) from seven GRB detectors. We found that VSGRBs form distinct class of GRBs, which in our opinion, in most cases can originate from the evaporating Primordial Black Holes (PBHs).

7. Oct 5, 2015

Chalnoth

We'll see. This is the kind of thing that will take time and diverse evidence to sort out. It'd be amazing if it held up, though. PBH evaporation could potentially be a window into quantum gravity.

8. Nov 4, 2016

1oldman2

http://www.nature.com/news/axion-alert-exotic-particle-detector-may-miss-out-on-dark-matter-1.20925

Early calculations had suggested that the axion should have a mass of around 5 microelectronvolts (µeV), about 100 billion times lighter than the electron, says Pierre Sikivie, a theoretical physicist at the University of Florida in Gainesville. So he and his collaborators designed ADMX to be most sensitive to masses in that range.

But in a paper published on 2 November in Nature1, Zoltan Fodor, a theoretical physicist at the University of Wuppertal in Germany, and his collaborators report the results of a large, complicated calculation showing that - under certain assumptions - the axion’s mass is most likely to fall in the range between 50 and 1,500 µeV. That would put it outside the range of ADMX, which is currently sensitive to masses between about 0.5 µeV and 40 µeV. "I think it is not very good news for ADMX," Fodor says.

9. Nov 5, 2016

nikkkom

I'd hazard to predict that DM particles are right-handed neutrinos (the "usual" ones, from SM minimally extended to have not only left-, but also right-handed neutrinos).

10. Nov 5, 2016

Chronos

PBH's fail rather miserably as DM candidates on a number of grounds, not just on the basis of gamma ray background surveys. For a fairly exhaustive discussion, see the seminal paper; https://arxiv.org/abs/astro-ph/0406095, The Cosmic Energy Inventory. Unshockingly enough, the possibility, however, cannot be entirely eliminated as discussed in this more recent paper; https://arxiv.org/abs/1607.06077, Primordial Black Holes as Dark Matter. and further discussed here; http://www.nasa.gov/feature/goddard...etween-primordial-black-holes-and-dark-matter. As usual, cold water is inexorably drawn to inflammatory ideas as discussed here; http://www.forbes.com/sites/startsw...-heres-why-the-idea-falls-apart/#4c07000c6d7b. The old adage: 'Nothing is certain in science.' remains appropriate. While I'm partial to a witch's brew that includes everything from black holes to exotic particles, that kind of explanation is viscerally repugnant to those with a fixation on order and beauty.

11. Nov 7, 2016

Chalnoth

It's pretty difficult to have multiple different dark matter components that each make up a significant density fraction. It's possible, but requires a fair amount of fine tuning.

I have no doubt that there are multiple components, but I'd say there's good reason to think that most likely 90%+ is made up of a single type of thing.

But if we can find one component of dark matter, and nail down its properties very precisely, then we should be able to determine whether or not there are other components needed to fill the mass budget. That won't be an easy estimate to make, but it should be doable.

12. Nov 7, 2016

Chronos

The notion of complexity in the dark sector has been gaining traction over the past couple of decades as discussed here; https://arxiv.org/abs/1504.03388, The behaviour of dark matter associated with 4 bright cluster galaxies in the 10kpc core of Abell 3827. A more recent discussion can be found here; https://arxiv.org/abs/1610.05327, Looking for dark matter trails in colliding galaxy clusters. To paraphrase Einstein: a good scientific theory should be as simple as possible, but not simpler. A one particle fits all explanation for DM may be inconsistent with this principle.

13. Nov 7, 2016

Chalnoth

I don't see what either of those papers have to do with the possibility of multiple dark matter species. It looks like they're using galaxy cluster data in an attempt to determine how dark matter scatters with itself. I don't see any discussion of multiple dark matter species. Certainly this kind of data could potentially aid in measuring the properties of multiple species (though not easily, and not without lots of other, independent data). But I don't see how it can help directly.

14. Nov 7, 2016

Chronos

Perhaps these papers are more representative; https://arxiv.org/abs/1404.3362, Beyond the ΛCDM cosmology: complex composition of dark matter, and, https://arxiv.org/abs/1512.05349, ETHOS - An Effective Theory of Structure Formation: Dark matter physics as a possible explanation of the small-scale CDM problems.

15. Nov 8, 2016

Doctor Strange

Is Dark Matter even disprovable at this point? Every time we fail to detect it, the theorists move the line. When we failed to find ether, we didn't turn around and imagine some new property that made it undetectable, we moved on to another theory having satisfied the principals of the Scientific Method. But after LUX, the common refrain is "The experiment constrained the energy of a DM particle" like it was some sort of confirmation rather than a negative result. At this point, how is it materially different to say that Dark Matter must be some form of exotic matter that is just out of view from our experiments and saying that 'God' provides the missing mass?

Last edited: Nov 8, 2016
16. Nov 8, 2016

nikkkom

Direct DM detection experiments also are not detecting neutrinos (because they are not sensitive enough yet to do so). And yet, we know for sure that neutrinos exist.

17. Nov 8, 2016

Doctor Strange

This is a poor example. Neutrino detectors work almost the same way that LUX works: you put a fluid deep under the earth and wait for some sort of radiation that indicates a weak interaction. So, yeah, neutrinos can be detected using this indirect method and, no, the same general idea has failed to find a dark matter candidate. And if you want to get technical, the Higgs Boson can't be detected directly, just through a statistical blip in other reactions. There's been no such 'blip' for DM in any (repeatable) experiment.

Last edited: Nov 8, 2016
18. Nov 8, 2016

nikkkom

Standard Model was not existing in this form from time immemorial. At first, there were three quarks. Then four. Then the third generation of both leptons and quarks was added.

Nothing guarantees SM will never be extended again. Right-handed neutrinos are likely candidates for next expansion, other ideas are being floated around.

19. Nov 8, 2016

Chronos

There is compelling body of evidence suggesting a significant mass deficit exists on large scales [galaxies and beyond], which leaves us only two logical explanations; 1] there is a huge unidentified, and, at best, weakly interactive component in the mass budget of the universe, or, 2] our theories of gravity are fundamentally flawed. Relatively few scientists are willing to concede existing evidence justifies a major revision to gravitational theory. Explanations that invoke more questions than they answer are rarely an effective approach. What you do not see is often as, if not more, revealing than what you do see.

20. Nov 8, 2016

Doctor Strange

3] The laws of motion are incomplete. But instead of letting the data lead you to the answer, you continue to force the data into the places you've already been. The fact that you (Cosmologists) can't even consider a change to the laws of motion is part of the problem.

Last edited: Nov 8, 2016
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