# Dark matter candidates, what chances would you give them?

1. Mar 6, 2006

### EL

What chances would you give the different candidates to actually make up (the major constituent of) the dark matter? That is, if you were a bookmaker, what chances would you find appropriate?
I'd find it interesting to see what you all think.

At the moment I'll go with the following:

LSP (50%)
K-K DM (5%)
Axions (4%)
Sterile neutrinos (2%)
Mond (2%)
General relativity, more careful calculations (1%)
Misinterpreted data, no dark matter needed (1%)
Not yet suggested dark matter particle (15%)
Other not suggested reason (15%)
Other suggested reason (5%)

2. Mar 6, 2006

### Garth

I guess I go with the "Other suggested reason (5%)", my suggestion being that all DM is baryonic produced in a Freely Coasting Model (FCM) as delivered by http://en.wikipedia.org/wiki/Self_creation_cosmology [Broken].

My suggestion to then explain where all this unseen baryonic matter resides is that roughly half of it is WHIM and roughly half IMBH's.

However I wouldn't want to put a percentage on it. The question is how well do these alternatives match up with the observed cosmological constraints. The GP-B experiment will sort out a few alternatives in about a year's time.

Garth

Last edited by a moderator: May 2, 2017
3. Mar 6, 2006

### EL

Sure, but what if you actually were a bookmaker? What odds would you decide? I mean you certainly would not put 100% on your own theory (couse in that case I would bet a lot of money you were wrong... )

4. Mar 6, 2006

### Garth

You might just lose it!

Seriously, while there are problems with the standard model, not least not being able to identify a Higgs Boson/Inflaton, DM particle or DE in the laboratory, other viable alternatives ought to be studied - just in case.

Garth

Last edited: Mar 6, 2006
5. Mar 6, 2006

### yanniru

DM Constituents

Since I am a layman, I have no right to do this.

Nonetheless, I put my money on a mixture of several components:

LSP
Axions
Mirror Matter

but hedge my bet with Bekenstein's MOND

6. Mar 6, 2006

### EL

Sure, no doubt about that. Until we find the answer, all candidates not violating current constraints should be kept in mind. However, what I was looking for was people's personal trust in different candidates.
Even though it may not be "scientifically correct" to rank the candidates, I would like to see what people think, just for fun...

7. Mar 6, 2006

### Chronos

I would like to place a side bet on WIMPS.

8. Mar 7, 2006

### EL

Ok, but what chances do you give them?

9. Mar 7, 2006

### Chronos

Fairly good. It would explain why we have so much difficulty detecting then in particle colliders.

10. Mar 7, 2006

### EL

You're all so scientifically moderate...
What should I do to get some numbers out?:tongue2:

11. Mar 7, 2006

### jimpy

General Relativity was and remains an inspired 100 year old guess at the way things might be,only Albert Einstein(in later years dominated by divine convictions) really believed it to be the basis of the TOE.The nature of electrons,the existence of protons and the likelihood of a singular initial condition set were outside it's ambit.It presents a chillingly effective predictive algebra for narrow midz-one phyics,effectively it is local curve fitting.Go down to Planck radius or move moderately towards galactic size and the theory has no physics to accompany the expectations and predictions it makes.Dark matter is a conjectural condition,aberrations of incomplete older theories should not drive clear thinking.The candidate formally missing from your list does not involve more accurate partial theories it should be "Inadequacies of early incomplete or approximate theories to represent physical realities"and a logical response would be to see this rated at 70%

12. Mar 8, 2006

### Chronos

Hi jimpy, welcome to PF. I think you would find almost everyone agrees current theories are incomplete, and the likely reason it has been vexingly difficult to unite GR and QM. On the other hand, both theories are amazingly predictive at macroscopic [GR] and plankian [QT] scales. So most people are fairly certain the correct unified theory will reduce to QM at planckian scales and somehow emerge as GR at macroscopic scales. As in most human endeavors, time is the enemy. It is essentially irrelevant in quantum theory, yet indispensible in GR.

Dark matter, however, is very much still alive these days. The fact it has not been detected in the lab is not a valid objection. Consider how long it took to validate the atom conjecture in human labs. If dark matter were a mathematical artifact introduced by a flawed theory of gravity, it would have a decidedly systematic effect on observation. But this is not observed. The evidence indicates non-baryonic matter [CDM] is just as clumpy and chaotically distributed throughout the universe as is baryonic matter. The only thing they appear to have in common is gravitational affinity - i.e., they tend to be drawn to one another. Find a big clump of baryonic matter, and it is almost a cinch you will find evidence it is embedded in an even bigger clump of CDM. The only variable is how much CDM appears to be hanging out in the hood. Oddly enough, this is frequently used to criticize the CDM conjecture - just add the right amount of CDM and all gravitational anomalies magically disappear. But isn't that exactly what you would expect if CDM really does exist - a variable amount at different locations? I would find it truly bizarre [and unbelievable] if every galaxy had the same proportion of CDM v baryonic matter. Pardon my rambling, but this is an interesting issue with many side bars to consider. Driving a stake through the heart of dark matter is simply not doable given current observational evidence - which is abundant and strikes from many directions. Science is hard. Ideas are more easily embraced than abandoned - as demonstrated by history.

Footnote - you may find this interesting:

Dark matter: A phenomenological existence proof
http://www.arxiv.org/abs/astro-ph/0601489

Last edited: Mar 8, 2006
13. Mar 8, 2006

### EL

Hi jimpy.
My list wasn't supposed to be exhausting, so everyone should feel free to come up with their own suggestions. It just reflects my current personal guess. Anyway, what you are looking for I would place under "Mond", something I have given a 2% chance to explain the dark matter problem.
Trying to build Mond theories at the scales were we observe the dark matter problem without being in conflict with current measurements has turned out to be pretty hard, and that's why I find other candidates much more likely to make up the dark matter. Of course GR has it's range of validity, but "at the scale of the dark matter problem" I find it probable to be trustful.
Btw, how would you divide your other 30%?

Last edited: Mar 8, 2006
14. Mar 8, 2006

### Labguy

I would too. Any random early formation on a large scale would be very unlikely to "parcel-out" equal proportions of matter, dark or otherwise, to what we can see today as different galaxies/clusters/superclusters. Small scale H, He and Li seem to fit initial BB conditions though and there is a fair bit of observational evidence to make that era "mainstream" today. I do see, though, a lot of mass-relation studies going on today but have to think that those that seem to indicate a constant proportion would be just as prevalent as those that don't show the same relation/proportions.
I would go with that also. No confirmed detection yet so there is also no known limit on an upper mass and/or lifespan. If there is no limit on the mass of virtual particles from the vacuum fluctuation as per Heisenberg (there isn't a limit) then WIMPS could be very massive and often replaced with similar mass after kicking the bucket. It all isn't just going to be electrons and positrons or quark-antiquark pairs.

Also, place emphasis on the "I" in WIMP for "Interacting". If they interact (and exist) then would we always have to think "non-baryonic"? I'm not a fan of wierd and mysterious matter lurking around in a universe blasted out of baryonic matter. Mysterious energy maybe, but not matter..

15. Mar 8, 2006

### EL

Could you please elaborate this, maybe I'm just getting you wrong. Why does non-baryonic (dark) matter sound mysterious to you? I mean, we have found plenty of it already...

Last edited: Mar 8, 2006
16. Mar 8, 2006

### Labguy

We have seen evidence for the existence of "dark matter", but there are also other theories floating about about MOND, adjusted GR, etc. that may not require DM at all.

But, if we accept DM, what do we have to show (yet) that it is specifically non-baryonic?

17. Mar 8, 2006

### EL

E.g. constraints from the BB nucleosynthesis which only allows baryonic matter to make up a few percents of the total energy density in the universe.

18. Mar 8, 2006

### Labguy

But maybe all the rest is energy. BB nucleosynthesis can be up to 10% baryonic matter (Ned Wright) but remember I first mentioned virtual particles from vacuum fluctuations. Also, all DM is most likely not to be of a single type; neutrinos can also contribute and they are "non-baryonic". With non-baryonic being defined as:
I guess that would even include WIMPS and many particle-antiparticle VP pairs. So, by that definition I could agree that the DM is likely to be non-baryonic (atoms/elements), but not likely to be a type of matter unknown (or mysterious) to us. Maybe "non-atomic" would be a better description, but many of the known sub-atomic particles, already existing and virtual, are "real" particles known to us and could be candidates for DM. It seems the only requirement for all candidates is that they are gravitationally affected, hence their probable detection.

19. Mar 8, 2006

### EL

That's a much higher percent than what is commonly accepted. Do you have a link to the paper?

This is consideder as a potential source of the dark energy.

Sure they can, and for a while they were a hot candidate. However, we now know they can just make up some percent or so of the total energy density. I.e. they have practically been ruled out.

Of course that includes WIMPS, which are the standard example of non-baryonic dark matter.

So you can agree WIMPS is a good candidate, but you don't like unknown candidates? In, that case, which WIMPS are you speaking of?

20. Mar 8, 2006

### Garth

We have?

We have plenty of evidence of Dark Matter. The only reason that this is said to be non-baryonic is the limitation on baryonic density by the standard model BBN as you later said EL.

If we are prepared to invoke undiscovered species to make the model fit perhaps we ought also to be prepared to consider alternative BBN models such as the “Freely Coasting” model, which do not need to invoke such undiscovered species as it identifies DM as baryonic.

Garth

Last edited: Mar 8, 2006
21. Mar 8, 2006

### Labguy

Wright's FAQ:
http://www.astro.ucla.edu/~wright/cosmology_faq.html#DM
Same Guy:
and we now know that they do have mass.

Any that haven't been confirmed. Do you have have a list of confirmed WIMPS for me?

22. Mar 8, 2006

### SpaceTiger

Staff Emeritus
WMAP also places a constraint on the baryonic density and gives similar numbers to those from nucleosynthesis.

23. Mar 8, 2006

### Gerinski

If non-baryonic DM is attracted gravitationally to baryonic matter, why do we always think of it just hovering in deep space, surrounding the galactic halos or making up filaments around galaxy clusters?

Shouldn't it also have got merged with the ordinary stuff everywhere, even right here where we are?
If non-baryonic DM gets merged with ordinary matter, even if it does not interact chemically or electrically or nuclearly with it, wouldn't it stay attached to it by gravitational attraction, however weak this is?

So, shouldn't the Earth itself, or the Sun, or whatever ordinary body around us, contain also non-baryonic DM?

And even if that answer is no, IF non-baryonic DM gets merged with baryonic matter, which space among it would it occupy? would it maybe occupy intermolecular and/or interatomic space, making such baryonic body appear heavier (denser) than it actually is?

24. Mar 8, 2006

### Garth

Thank you, a good point.

However the interpretaiton of the WMAP data is model dependent.

For example are the peaks consistent with a spatially flat universe, as normally thought, or with a conformally flat one? If conformally flat then the total density $\Omega_{total}$ need not be ~ 1 and if finite then that could explain the quadrupole deficiency. Such a change in model would alter the cosmological parameter fit.

Secondly the calculation of the baryon density is convoluted with the primordial Deuterium abundance. This is fitted to the present epoch observed abundance as an upper limit as Deuterium is fragile and can be destroyed but not easily nucleosynthesised. However spallation in shocks, perhaps in the formation and demise of PopIII stars, can also produce Deuterium (Deuterium Production by High Energy Particles - Richard I Epstein Ap.J. 212 595-601 1977) and if this is significant then the Deuterium primordial abundance has been over-estimated and the baryon abundance consequently out.

The WMAP data is certainly consistent with an $\Omega_b = 0.04$, however it might also be consistent with a different value as indeed claimed by Gehlaut et al. for the Freely Coasting model.

Garth

Last edited: Mar 8, 2006
25. Mar 8, 2006

### EL

Neutrinos, electrons, positrons, muons...

No, it's not the only reason (but even if it was it would still be a very good one). As Spacetiger mensionen the baryon fraction can be extracted from the WMAP data (if I remeber it correctly, it mainly depends on the hight of the second peak in the power spectrum).
Also, simulations show that a large fraction of the matter must be non-baryonic in order for structures to form fast enough, something a baryon dominated universe would not be able to do.