View Full Version : Dark matter candidates, what chances would you give them?
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%)
I guess I go with the "Other suggested reason (5%)", my suggestion being that all DM is baryonic produced in a Freely Coasting Model (http://arxiv.org/abs/astro-ph/0306448) (FCM) as delivered by SCC (http://en.wikipedia.org/wiki/Self_creation_cosmology).
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 (http://physicsforums.com/showthread.php?t=104694&highlight=garth) experiment will sort out a few alternatives in about a year's time.
Garth
However I wouldn't want to put a percentage on it
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...:wink: )
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...:wink: )
You might just lose it! :biggrin:
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
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
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.
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...
I would like to place a side bet on WIMPS.
I would like to place a side bet on WIMPS.
Ok, but what chances do you give them?
Fairly good. It would explain why we have so much difficulty detecting then in particle colliders.
You're all so scientifically moderate...:smile:
What should I do to get some numbers out?:tongue2:
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%
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
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%
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%?
I would find it truly bizarre [and unbelievable] if every galaxy had the same proportion of CDM v baryonic matter.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 like to place a side bet on WIMPS.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..:confused:
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..:confused:
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...
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...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?
But, if we accept DM, what do we have to show (yet) that it is specifically non-baryonic?
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.
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.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: non-baryonic: not made up of neutrons, protons and electrons, and thus not like any of the known chemical elements. (anything made from atoms) 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.
But maybe all the rest is energy. BB nucleosynthesis can be up to 10% baryonic matter (Ned Wright)
That's a much higher percent than what is commonly accepted. Do you have a link to the paper?
but remember I first mentioned virtual particles from vacuum fluctuations.
This is consideder as a potential source of the dark energy.
Also, all DM is most likely not to be of a single type; neutrinos can also contribute and they are "non-baryonic".
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.
I guess that would even include WIMPS
Of course that includes WIMPS, which are the standard example of non-baryonic dark matter.
but not likely to be a type of matter unknown (or mysterious) to us.
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?
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...
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 (http://arxiv.org/abs/astro-ph/0306448), which do not need to invoke such undiscovered species as it identifies DM as baryonic.
Garth
That's a much higher percent than what is commonly accepted. Do you have a link to the paper?Wright's FAQ:
http://www.astro.ucla.edu/~wright/cosmology_faq.html#DM
But the theory of Big Bang nucleosynthesis says that the density of ordinary matter (anything made from atoms) can be at most 10% of the critical density, so the majority of the Universe does not emit light, does not scatter light, does not absorb light, and is not even made out of atoms. 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.Same Guy:
This "non-baryonic" dark matter can be neutrinos, if they have small masses instead of being massless, or it can be WIMPs and we now know that they do have mass.
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?Any that haven't been confirmed. Do you have have a list of confirmed WIMPS for me?
SpaceTiger
Mar8-06, 01:30 PM
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.
WMAP also places a constraint on the baryonic density and gives similar numbers to those from nucleosynthesis.
Gerinski
Mar8-06, 03:00 PM
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?
WMAP also places a constraint on the baryonic density and gives similar numbers to those from nucleosynthesis.
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
We have?
Neutrinos, electrons, positrons, muons...
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.
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.
and we now know that they (neutrinos) do have mass.
We have known that for a while now, and people have calculated what fraction they may make up, and we have concluded that neutrinos can only make up a few percent of the total energy density of the universe. Hence they can just make up a small part of the dark matter.
Any that haven't been confirmed. Do you have have a list of confirmed WIMPS for me?
Of course not. There are no confirmed WIMPS. And that is why I asked that question: Why are you willing to accept WIMPS as a good candidate, but not new species of non-baryonic matter? I mean, WIMPS are new species of non-baryonic matter...
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?
But we aren't...
Shouldn't it also have got merged with the ordinary stuff everywhere, even right here where we are?
Sure. The dark matter should be all around us, and there are plenty of experiments around the world trying to detect it.
So, shouldn't the Earth itself, or the Sun, or whatever ordinary body around us, contain also non-baryonic DM?
There should be an excess of DM around strong gravitational sources (e.g. the sun. or why not even better: the galactic centre). However a DM particle propagating in the direction towards a massive body, will certainly just pass through it, just like neutrinos do.
Hence they can just make up a small part of the dark matter.That was my point when I said DM won't turn out to be of just one type. Neutrinos, some WIMPS, a bit of undetected baryonic matter, a pinch of salt, some tabasco, etc. Why are you willing to accept WIMPS as a good candidate, but not new species of non-baryonic matter?What new species? I've already mentioned that I think some will be massive particles formed by vacuum fluctuations. If some other particles are found to be massive enough to count and interact (with gravity) then they would be WIMPS, no? Maybe in the future we'll have sub-classes of WIMPS. Everything new we may find will have to be named something.
ole El,
I have a quotation from another time:
"-we have not to discover the properties of a thing which we have recognised in nature but to discover how to recognise in nature a thing whose properties we have assigned.This development seems inevitable;but it has grave drawbacks especially when theories have to be reconstructed.Fuller knowledge may show that there is nothing in nature having precisely the properties assigned;or it may turn out that there is nothing in nature having precisely the properties assigned;or it may turn out that the thing having these properties has entirely lost it's importance when the new theoretical standpoint is adopted..."
Mond theories are a convenient baggage receptacle,the wisdom of yesterday is often inconvenient when it gets in the way.
I only take issue with the 1-2% versus my 70%.The rest is fine
Neutrinos, electrons, positrons, muons...
Come on.. we are talking about \Omega_{DM} \sim 0.23 here!
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).
Well as I replied to SpaceTiger, the conclusions from WMAP are model dependent.
And as I said above the standard interpretation of that data would be more robust if it could be shown to be concordant with the deficient quadrupole.
Other models such as the FCM A Concordant “Freely Coasting” Cosmology (http://arxiv.org/abs/astro-ph/0306448) also claim to be concordant with the WMAP data. 3 Summary
The main point we make in this article is that in spite of a significantly different evolution, the recombination history of a linearly coasting cosmology can be expected to give the location of the primary acoustic peaks in the same range of angles as that given in Standard Cosmology.
.........................
[\Omega_b \sim 0.2]Thus linear coasting has the potential of relegating the need for any form of dark matter or dark energy (or for that matter, any physics not already tested in the laboratory) to the physics archives where they enjoy the same status as ether and phlogiston.
The message this article is to convey is that a universe that is born and evolves as a curvature dominated model has a tremendous concordance and there are sufficient grounds to explore models that support such a coasting.([] my insertion for clarity)
In that conclusion the authors should have added the caveat that the missing laboratory tested physics in the model is a gravitational theory that delivers the strictly linearly expanding universe. SCC (http://en.wikipedia.org/wiki/Self_creation_cosmology) provides that theory, and it is being tested by GP-B (http://physicsforums.com/showthread.php?t=104694) at this very moment.
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.
The FCM universe expands more slowly than the standard [itex]\Lambda[/tex]CDM model so there is more than twice the time available for structures to form at the high (>1) z epochs.
Garth
That was my point when I said DM won't turn out to be of just one type. Neutrinos, some WIMPS, a bit of undetected baryonic matter, a pinch of salt, some tabasco, etc. What new species? I've already mentioned that I think some will be massive particles formed by vacuum fluctuations. If some other particles are found to be massive enough to count and interact (with gravity) then they would be WIMPS, no? Maybe in the future we'll have sub-classes of WIMPS. Everything new we may find will have to be named something.
So maybe we're just talking around each other, but what I was reacting to was that I got the impression you didn't like the thought of non-baryonic dark matter:
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.
As we have argued, the known particle species will hardly make up any greater part of the matter density needed. This means that (if the dark matter problem is solved by particles, which I'm a great fan of) the DM has to be made up by some species we havn't found in the laboratory yet.
I can understand if you object to inwoking new particle species at all, but why would it be so strange if this new particle was non-baryonic?
I mean I can't see why non-baryonic particles are not in any way more "mysterious" that baryonic...
I only take issue with the 1-2% versus my 70%.The rest is fine
Well, I based my 2% on the fact that despite many attempts, no one (at least that I have heard of) have managed to cook up a mond theory consistent with observational data. Mond isn't a hot candidate in the scientific society at the moment.
Come on.. we are talking about \Omega_{DM} \sim 0.23 here!
But I wasn't talking about dark matter. I was just trying to make clear that non-baryonic matter is not in anyway stranger than baryonic, which I got the impression Labguy was saying.
Well as I replied to SpaceTiger, the conclusions from WMAP are model dependent.
Sure you are of course right about that, but I'm just not a fan of leaving mainstream models.
The FCM universe expands more slowly than the standard [itex]\Lambda[/tex]CDM model so there is more than twice the time available for structures to form at the high (>1) z epochs.
Interesting. Are there any simulations done? Will the FCM model account for the structures we observe today?
But I wasn't talking about dark matter. I was just trying to make clear that non-baryonic matter is not in anyway stranger than baryonic, which I got the impression Labguy was saying.
Okay, crossed posts, always a problem on PF!
Interesting. Are there any simulations done? Will the FCM model account for the structures we observe today?
I'm working on it! Actually I do not have the facilities to run such simulations, perhaps after GP-B comes up trumps :rolleyes: somebody else will do it for me. [Anybody out there willing to have a go?]
All I have done are 'back of the envelope' Jeans mass and free fall time estimations.
Garth
I can understand if you object to inwoking new particle species at all, but why would it be so strange if this new particle was non-baryonic?
I mean I can't see why non-baryonic particles are not in any way more "mysterious" that baryonic...Yo!, Stop!, Halt! and Alto!:
That part is my fault and from your other posts just above it seems we do agree. With WIMPS, neutrinos, mesons and even virtual particles all being known or soon-to-be-known (?) items and "particles", I was thinking (dangerous for me) "non-particle" instead of "non-baryonic". There is nothing at all mysterious about these particles not fitting the definition of baryonic that I posted before.
I started out by voting/betting with Chronos on WIMPS as a large candidate and mentally ruling out such things as large masses of anti-matter or any possibility of any EM or gravitational waves (gravitons?) etc. as having a property fitting the apparent observations indicating that DM is out there in great abundance.
It is all from my own foul-up of not paying attention to the difference in the definitions between baryonic and particle; I was just thinking too fast and too wrong! Anyone reading my posts should look at the signature first and then read the post..:cry:
But, I will still give a fair percentage of the various DM possibilities to virtual particles of any mass being formed from vacuum fluctuations. In their short-lived existence they would have a property affected by gravity, exert a gravitational influence and blink out with an energy return. If they are a seething and self-replacing mass, that might explain why they don't have the other observational properties (non-interacting) of baryonic matter that all DM is also lacking.
Is it possible that galaxies/clusters/superclusters is where DM is most easily detected because more energy (gravitational, magnetic/EM and angular momentum) is available there and therefore would lead to higher virtual particle production than more "empty" space?? (rhetorical question).
But, I will still give a fair percentage of the various DM possibilities to virtual particles of any mass being formed from vacuum fluctuations. In their short-lived existence they would have a property affected by gravity, exert a gravitational influence and blink out with an energy return. If they are a seething and self-replacing mass, that might explain why they don't have the other observational properties (non-interacting) of baryonic matter that all DM is also lacking.
Is it possible that galaxies/clusters/superclusters is where DM is most easily detected because more energy (gravitational, magnetic/EM and angular momentum) is available there and therefore would lead to higher virtual particle production than more "empty" space?? (rhetorical question).Vacuum polarization as a gravitational effect - exactly. With the very large calculated mass-equivalence of the quantum vacuum, it would be very surprising if it did not play a role in gravitation.
Gerinski
Mar9-06, 02:34 PM
Sure. The dark matter should be all around us, and there are plenty of experiments around the world trying to detect it.
There should be an excess of DM around strong gravitational sources (e.g. the sun. or why not even better: the galactic centre). However a DM particle propagating in the direction towards a massive body, will certainly just pass through it, just like neutrinos do.
Sorry, I'm just a layman beginner next to all of you here, but there's still something I don' get...
As far as I know, during the development of the Universe the main mechanism for matter aggregation into forming galaxies, solar systems, planets and so on has been gravity. The other forces do not act significantly until matter has got clumped very near to eachother.
If non-baryonic DM is maybe around 4 or 5 times more abundant than baryonic matter and it interacts gravitationally, it should have followed the same aggregation flow as baryonic matter, should't it?
or rather even, it should have been the baryonic matter getting aggregated to/towards (expectedly bigger) clupms of non-baryonic DM.
Why should't we expect the Earth (or any body) to be formed by a combination of non-baryonic DM and baryonic matter in a ratio of 4 or 5 to 1 ? (mostly by non-baryonic DM).
I can understand your point that if a non-baryonic DM particle travels towards a massive baryonic body, it may just pass through it because the gravitational attraction is not enough to slow down its inertial movement, but, in the grand scheme of matter aggregation to form structures in the Universe, I don't see why non-baryonic DM shouldn't have followed the same gravitational aggregation pattern that baryonic matter did. And once gravitationally bound, why should it fly away?
If the amount of non-baryonic DM was small (let's say 10%) compared to baryonic matter, I could understand that it may have mostly drifted appart.
But with a ratio of 4 or 5 to 1, one would expect that a significant part of any celestial body be composed of non-baryonic DM. And certainly such a big mass contribution would be detectable by gravitational effects?
Once again, it seems like it should have been more like the abundant non-baryonic DM dominating the gravitational aggregations, and the scarce baryonic matter just falling into it.
So it might be more likely to find galaxies of non-baryonic DM surrounded by halos of baryonic matter than the other way around!
I know I'm most likely wrong but please explain me why! :-)
I'm working on it! Actually I do not have the facilities to run such simulations, perhaps after GP-B comes up trumps :rolleyes: somebody else will do it for me. [Anybody out there willing to have a go?]
All I have done are 'back of the envelope' Jeans mass and free fall time estimations.
That's always a good starting point. Btw, when is gravity probe B planned to?
Yo!, Stop!, Halt! and Alto!:
:smile: Ok, so we were just misunderstanding each other somewhat.
However, I'm not sure I really get what you mean by virtual particles as a DM candidate. Could you elaborate more?
That's always a good starting point. Btw, when is gravity probe B planned to?
I'm getting masses of 108MSolar forming and fragmenting 106 yrs after recombination at 13 Myrs i.e. at 14 Myrs, the process finishing ~ 108 yrs. ~ z = 100.
The GP-B team will know late this summer but not publish until April 2007 after cross checking with outside authorities on the results.
Garth
These are some nice questions Gerinski. I'll try to give a short answer, but I'm sure someone else here can certainly fill in more details.
As far as I know, during the development of the Universe the main mechanism for matter aggregation into forming galaxies, solar systems, planets and so on has been gravity. The other forces do not act significantly until matter has got clumped very near to eachother.
Yes, but I think you underestimate the importance of these forces, which makes the difference between the structure formation of ordinary and dark matter.
If non-baryonic DM is maybe around 4 or 5 times more abundant than baryonic matter and it interacts gravitationally, it should have followed the same aggregation flow as baryonic matter, should't it?
No, see above. There's been plenty of simulations of structure formation from both WIMP dark matter and ordinary baryonic matter. Due to the difference in strengths of interactions other than gravity, they actually end up somewhat different, with DM more smoothly distributed.
I'm getting masses of 108MSolar forming and fragmenting 106 yrs after recombination at 13 Myrs i.e. at 14 Myrs, the process finishing ~ 108 yrs. ~ z = 100.
Ok. I admit I don't know what to expect just by hand. But I guess this is acceptable or?
The GP-B team will know late this summer but not publish until April 2007 after cross checking with outside authorities on the results.
I'll guess you are looking forward to April next year then...:wink:
I supposethat roger penrose,william clifford,felix klein,later oskar klein,earlier weyl et al might be really impressed with a curvature driven model.isn't that really the issue?
I'm getting masses of 108MSolar forming and fragmenting 106 yrs after recombination at 13 Myrs i.e. at 14 Myrs, the process finishing ~ 108 yrs. ~ z = 100.Ok. I admit I don't know what to expect just by hand. But I guess this is acceptable or?
The Jeans Length works out as 12000 lgt.yrs, i.e roughly one halo per ~ 104 lgt.yrs, or an average of one every 107 lgt.yrs. today.
If the density anisotropies are at the ~ 10-5 level and kinetic energies of forming halos follows the potential energy of these wells, their relative velocities would be expected to be of the order 10-2.5c, which is the OOM of our own galaxy's motion relative to the CMB.
To an OOM take a lower limit typical velocity for these halos to be ~ 10-3c, (300 km/sec), collisions between them would be expected every ~ 107 yrs.
About 104 mergers would be required to make up a typical spiral halo, or elliptical galactic, mass of 1012 MSolar.
Thus such halo masses might form after, a very hand waving estimate, ~ \sqrt N of 107 x 102 = 109 yrs, which would be seen today in the FCM model at z = 13, and onwards at lower z towards the present. This is where the earliest galaxies appear to have formed Detecting Reionization in the Star Formation Histories of High-Redshift Galaxies (http://arxiv.org/abs/astro-ph/0510421) Massive galaxies are routinely being detected at red-shifts z > 6 (Bouwens et al. 2005), in some cases with sufficient data for a detailed analysis of the stellar content. For example, Mobasher et al. (2005) have recently reported the discovery of HUDF-JD2, a galaxy which is potentially at z ~ 6.5, although spectral lines were not detected and thus the redshift is based on the shape of the spectrum.
If the high redshift is a correct inference, then the galaxy possesses almost 1012M⊙ in stars. Further analysis of the
spectral shape indicates that the galaxy formed the bulk of its stars at z > 9 and could have reionized its surrounding region at z > 10 (Panagia et al. 2005). Also, Eyles et al. (2005) analyzed two galaxies at z > 5.8 that had been found by Stanway, Bunker, & McMahon (2003). They showed that these galaxies had stellar masses of > 1010M⊙ and had formed most of their stars at z > 7.5 while a minority formed closer to the detected redshift.
I'll guess you are looking forward to April next year then...:wink:And how!
Garth
Looks not to bad...:smile:
How many people are actually looking at this FCM model? Hard to persuade someone to do some simulations before GP-B?
Gerinski
Mar10-06, 02:20 PM
Yes, but I think you underestimate the importance of these forces, which makes the difference between the structure formation of ordinary and dark matter.
No, see above. There's been plenty of simulations of structure formation from both WIMP dark matter and ordinary baryonic matter. Due to the difference in strengths of interactions other than gravity, they actually end up somewhat different, with DM more smoothly distributed.
Do you mean that (for example) the particles making up the Earth, were it not for the EM and nuclear forces, would not make up a stable "solid" body?
That gravity alone wouldn't be strong enough to hold them together and the Earth would evaporate into cosmic particle dust?
On the other hand, one reads frequently statements such as "the size of stars is determined by a delicate balance between the outward forces of the nuclear reactions and the inwards force of gravity. When a star consumes its fuel, gravity wins the game and collapses it into a white dwarf, a neutron star, a black hole or whatever"
Such statements make one feel that gravity is not so weak after all, and that it's perfectly sufficient to hold together a big enough clump of matter (of course the stellar matter also interacts among itself by EM and nuclear forces, but the refered reason for collapse is always gravity).
So still, I don't quite understand why did not the non-baryonic DM aggregate by gravity into "solid" DM bodies, with additional baryonic matter aggregating further into them.
So still, I don't quite understand why did not the non-baryonic DM aggregate by gravity into "solid" DM bodies, with additional baryonic matter aggregating further into them.
Non-baryonic DM is mysterious stuff, it is given just the right ad hoc properties to fit the cosmological constraints, but what are those constraints and what properties are required to meet them?
It is generally 'non-interacting' so it doesn't form DM 'planets' etc, just deep gravitational potential wells into which ordinary stuff can fall. However, that doesn't quite fit, and so it is thought to be 'weakly interacting' so it doesn't form too deep a well in galactic centres (the 'cuspy' problem).
You need to find a miracle cure that will produce the correct large scale structure and the correct local galacic halo profiles, but what it doesn't do is interact with itself so strongly that it condenses down into ""solid" DM bodies."
On the other hand, it is important to realise that until we have identified the DM particle in a laboratory, (LHC?) measured its properties and found they match the cosmological and astronomical constraints, we do not really know what we are talking about!
Garth
Non-baryonic DM is mysterious stuff, it is given just the right ad hoc properties to fit the cosmological constraints, but what are those constraints and what properties are required to meet them?
I would not completely agree with this. For example, looking at a specific dark matter candidate: the LSP, lightest supersymmetric particle. The LSP arises in particle physics as an attempt to solve another problem (the hierarchy problem) which is not connected with cosmology. From the theory of supersymmetry it then happens that the LSP in fact have the right properties to be a DM candidate.
That's what I find beautiful about LSP-DM; it is not just an "ad hoc" particle needed for solving the DM, but actually arises from a completely different problem.
Okay - I stand corrected.
EDIT - I hadn't realised the LSP had been detected! :smile:
We will see whether the LSP does last the course.
Garth
Chronos
Mar12-06, 03:17 AM
EL, I can think of only a few dozen humans on planet earth who would so easily make that connection - and most of them work at CERN.
EDIT - I hadn't realised the LSP had been detected! :smile:
That's something I've NEVER said.
If it wasn't for the fact that dark matter particle candidates pop up out of theories needed to solve other non-related problems, I would of course be much more sceptical.
EL, I can think of only a few dozen humans on planet earth who would so easily make that connection - and most of them work at CERN.
Que? The LSP is probably the most popular candidate of them all.
Note that I'm not saying it has to be the solution, just the most probable one in my opinion...
I find it more pleasant to inwoke new particles we have hints for that they should exist, than modifying our basic physical laws...
EDIT - I hadn't realised the LSP had been detected! :smile: That's something I've NEVER said.
If it wasn't for the fact that dark matter particle candidates pop up out of theories needed to solve other non-related problems, I would of course be much more sceptical.
I was pulling your leg!
But the serious point is that we need to identify the DM particle in the laboratory, measure its properties and prove they are concordant with the cosmological constraints and then and only then will we know what we are talking about.
It is this lack of confirmation that continues to render the standard \Lambda CDM model provisional.
GArth
turbo-1
Mar12-06, 05:00 PM
There has been a tremendous expenditure of resources of all types (including peoples' entire careers) thrown at this problem, but I have a question. Why are we building higher-energy colliders to look for the LSP? The concentration should be on the building of detectors, because if the the LSPs exist, they should be everywhere. If lightest supersymmetric particle is truly the lightest, there is no lighter supersymmetrical particle that it can decay to, meaning that if they exist, the universe should be teeming with them already. Every one ever produced still exists - they are immortal. The fact that LSPs have not been detected already should be sobering to the guys building and equipping the collidors. Has this been discussed in the literature, EL?
I was pulling your leg!
Yeah, I noticed that, just had to defend my case anyway...My capital letters maybe were too much, or at least I should have added a smiley in the end...so I'll do it now instead...:cool:
But the serious point is that we need to identify the DM particle in the laboratory, measure its properties and prove they are concordant with the cosmological constraints and then and only then will we know what we are talking about.
Of course. But that's the way it goes for every suggested solution to the problem: We have to find a way to measure its validity!
It is this lack of confirmation that continues to render the standard \Lambda CDM model provisional.
Yepp, as well as all others...
There has been a tremendous expenditure of resources of all types (including peoples' entire careers) thrown at this problem, but I have a question. Why are we building higher-energy colliders to look for the LSP?
Well, the LSP is just one out of plenty of reasons why we build colliders like LHC. Maybe the most interesting to come out of LHC is something we had not even thought about. But anyway, let's move on:
The concentration should be on the building of detectors, because if the the LSPs exist, they should be everywhere.
Sure, and there are a lot of experiments running and being developed for direct detection. These will probably reach enough sensitivity to scan at least some part of the LSP parameter space in a few years. Besides particle physics constraints on the cross section for interaction with the detector, the chance of succeeding also highly depends on astrophysical conditions; we're not exaclty sure of what local density of DM particles to expect. If we're lucky we'll find some evidence for DM through direct detection even before LHC, but due to that the LSP probably interacts very tiny with ordinary matter I personally doubt that.
However, once (and if!) we find the LSP at CERN we of course also need to confirm that it really makes up the DM, so direct detection is of course needed for the complete confirmation.
If lightest supersymmetric particle is truly the lightest, there is no lighter supersymmetrical particle that it can decay to, meaning that if they exist, the universe should be teeming with them already. Every one ever produced still exists - they are immortal.
You're are right to a certain extent. The LSP is forbidden to decay into other particles through a multiplicative quantum number called R-parity which is conserved in supersymmetric theories. (Well, actually there are SUSY theories without conserved R-parity, but for several reasons those are not as intersesting, but let's keep this simple.) Ordninary particles have R-parity (1) while their supersymmetric partners carry (-1). That's why a single LSP cannot decay into anything less massive. However, two particles with R-parity (-1) each, that is a total of (-1)*(-1)=(1) can annihilate into a standard model pair, like two gammas. Observing these gammas (for example from the dense region in the galactic centre) in fact is a way to indirectly detect the LSP, and much work has been put down on clearing such things out too. However it's not clear wheter this signal will drown into the background from other astrophysical sources.
The fact that LSPs have not been detected already should be sobering to the guys building and equipping the collidors.
The missing signal from direct detection of course puts limits on what properties the LSP might have, but the parameter space where the LSP can be is still HUGE, and direct detection need to become much more efficient before it can rule out the LSP as a DM candidate.
Has this been discussed in the literature, EL?
Oh yeah, in hundreds, maybe more, papers over the years. A good one to start with is maybe Jungman et al:
http://www.arxiv.org/abs/hep-ph/9506380
It's certainly not up to date, but the concepts are nicely explained.
turbo-1
Mar12-06, 07:08 PM
Please allow me to clarify, EL. When I asked if "this has been discussed on the literature", I was refering not to "LSP as Dark Matter", which is self-evident, but to the concept that the current non-detection of LSP is a problem for the Standard Model.
I have a very compelling reason to believe that there is no Graviton, no Higgs Boson, no SUSY particles, etc, which I cannot elucidate here due to forum rules, so this is an important subject for me.
When I asked if "this has been discussed on the literature", I was refering not to "LSP as Dark Matter", which is self-evident, but to the concept that the current non-detection of LSP is a problem for the Standard Model.
But it is not a problem for the Standard Model that the LSP has not been detected yet. Why should it be?
turbo-1
Mar12-06, 07:50 PM
But it is not a problem for the Standard Model that the LSP has not been detected yet. Why should it be?Because the LSP (if it exists) should permeate the Universe, and even if it is extremely weakly interactive, the odds are that we should have seen some hints that they exist. So far, none yet.
Chronos
Mar12-06, 08:39 PM
The lack of detection is not an issue in the minds of most theorists. Historical, some ideas take longer than others to meet the burden of proof. The atom is a good example. First conceived by Democritus in 460 BC, their detection was not achieved until around 1803: when Dalton conducted experiments suggesting matter was indeed composed of elementary, tiny particles [atoms]. Even so, it was another century before Rutherford and Wilson achieved the first real 'proof' of the atom.
Neutrinos [the other dark matter] also proved elusive. Pauli predicted their existence 1931. First detection was not achieved until 1959 by Cowan and Reines, and the elusive tau neutrino was not detected until 2000. Researchers did not give up on the neutrino for the same reasons they have not given up on their more introverted DM relatives.
turbo-1
Mar12-06, 10:01 PM
The lack of detection is not an issue in the minds of most theorists.This is a problem. If your cosmology is hanging on something that has never been detected (even tentatively) then the theorists need to study obervations for a bit and come up with some new speculations. If theorists are allowed to frame the question and reject all observations that conflict with their assumptions, we are in a very unhealthy situation.
Because the LSP (if it exists) should permeate the Universe, and even if it is extremely weakly interactive, the odds are that we should have seen some hints that they exist. So far, none yet.
What you are are saying is simply not correct.
Theory of supersymmetry, together with simulations telling us what local density of DM we could expect, indeed favours the situation that we have not yet detected the LSP! With current experiments we have just started to scratch the surface of the huge parameter space where the LSP could live.
However, with the LHC together with future direct detection experiments, a major part of the parameter space can be searched trough.
You can read about all this in the Jungman link I gave you.
If theorists are allowed to frame the question and reject all observations that conflict with their assumptions, we are in a very unhealthy situation.
But theorists don't reject any observations, where have you got that from?
Instead all observations and experiments put limits on the theory, i.e. they reduce the parameter space of the LSP.
(Here are some recent results: http://www.arxiv.org/abs/hep-ph/0602028 )
For every new experiment/observation the parameter space is cut down by another small amount, but there's still a huge piece left over.
Again, you can also read about this in Jungman.
turbo-1
Mar13-06, 08:56 AM
EL, you posted a link to Jungman's table of contents, not to the paper, and the embedded URLs in the abstract do not work either. I tried Googling on "Supersymmetric Dark Matter" and got over 40,000 hits - too many to wade through. Do you have a link to the full PDF?
EL, you posted a link to Jungman's table of contents, not to the paper, and the embedded URLs in the abstract do not work either. I tried Googling on "Supersymmetric Dark Matter" and got over 40,000 hits - too many to wade through. Do you have a link to the full PDF?
Oops, sorry for that:redface: . No I don't have a link to the PDF, but I managed to download it from Physics Reports. However if you don't have access to that journal it may be hard to find it for free (leagaly).
Try this paper by Bergstrom instead:
http://www.arxiv.org/abs/hep-ph/0002126
It's not as detailed as Jungman, but instead easier to follow, and somewhat more up to date (although a lot has happened during the last years). Check out chapter 8-9 in specific.
SpaceTiger
Mar13-06, 01:03 PM
Because the LSP (if it exists) should permeate the Universe, and even if it is extremely weakly interactive, the odds are that we should have seen some hints that they exist.
Oh really? Could you please show us this calculation?
turbo-1
Mar13-06, 02:49 PM
Oh really? Could you please show us this calculation?http://arxiv.org/PS_cache/astro-ph/pdf/0504/0504241.pdf
For WIMPs with masses of approximately 100 GeV/c2 (the mass of a A=100 nucleus, we will see later the motivation for this example), the local density is 3000 WIMP per cubic meter, and a flux of 6x104 WIMPs is traversing each cm2 of our body every second. Another important aspect is that the average kinetic energy of these WIMPs is 20 keV.If the LSP can self-annihilate in pairs, the energy released in such annihilation should be pretty significant, with a "signature" energy or energies (depending on the nature of the decay particles). If the LSP is truly "weakly interactive" it cannot be excluded from the detectors of the accelerators around the world, yet such an annihilation event has never been observed (or at least none have been recognized and reported, to my knowledge). With such a high WIMP flux impinging on detectors at accelerators, shouldn't we have observed WIMP annihilation serendipitously by now? It would appear as if the decay particles arose spontaneously, with excess energy carried of as gamma rays.
If the LSP can self-annihilate in pairs, the energy released in such annihilation should be pretty significant, with a "signature" energy or energies (depending on the nature of the decay particles).
People have investigated what signatures to expect. See for example:
http://www.arxiv.org/abs/hep-ph/0507229
However, it's not clear wheter it will completely drown into the background from other astrophysical sources or not.
If the LSP is truly "weakly interactive" it cannot be excluded from the detectors of the accelerators around the world, yet such an annihilation event has never been observed (or at least none have been recognized and reported, to my knowledge). With such a high WIMP flux impinging on detectors at accelerators, shouldn't we have observed WIMP annihilation serendipitously by now? It would appear as if the decay particles arose spontaneously, with excess energy carried of as gamma rays.
First of all: The DM direct detection detectors are not part of any accelerators. Detectors in accelerators are design to detect what's produced in the accelerator. Direct detection detectors are designed somewhat similar as neutrino detectors. For example Edelwise (which is mensioned in your quoted paper) is situated several kilometers inside a mountain, at the border between France and Italy (actually I recently visited Edelwise), in order to reduce the background.
For the second: Have you even taken your time to read the paper you're citing? In section 4.5 it says:
"As current experiments are more than four order of magnitude away from a full coverage of the bulk of supersymmetric predictions, the coming years may reveal that the ultimate sensitivity can only be reached by detector techniques that are now in a very early development stage."
And in the conclusions it clearly states:
"there is still a lot of development in progress on the road to the 10^−8 pb sensitivity of current projects to the ultimate 10^−10 pb sensitivity necessary to cover most of the MSSM domain."
That is, we need to get to 10^-10 pb sensitivity before most of the LSP parameter space can be covered by direct detection experiments.
At the moment we are, as said before, just scratching the surface.
For the third: Were is the calculation Space Tiger asked for? All your cited paper succeeded with was to completely debunk your own claims.
Suggested reading is still the Bergstrom paper I linked. Please feel free to ask about things you don't find clear.
SpaceTiger
Mar13-06, 04:50 PM
http://arxiv.org/PS_cache/astro-ph/pdf/0504/0504241.pdf
An excellent link, thank you turbo-1. Unfortunately, you seem to have seriously misinterpreted the paper. Skip ahead to section 3.4, titled "Current status of direct searches":
At present, the most competitive direct searches have reached sensitivities close to 10-6 pb. This starts to explore the domain of optimistic supersymmetric models.
In other words, the majority of WIMP candidates from theories of supersymmetry are undetectable by these experiments.
turbo-1
Mar13-06, 05:26 PM
Maybe I wasn't clear. Direct detection of LSP may be some time away, but given the flux density of this proposed DM candidate, should we not have seen (serendipitously) the spontaneous production of the decay products of the LSP in at least some accelerator detectors by now? If the decay products and the energy released falls in the mass range of the LSP, that would be a very good indirect detection, and help nail down the sensitivities needed for direct detection. If the LSP is indeed weakly interactive, there is no way to exclude those particles from the detector chambers. Certainly the people monitoring that equipment have an idea what such a serendipitous observation should look like, including a range of energies that might be released.
We shouldn't have to concentrate on trying to make these WIMPS if they are as plentiful as expected. We should simply start watching for pair-decay. If the Standard Model is correct, the Universe has already produced all the LSPs we need and we can use existing detectors to watch for the decay of the LSPs, which will appear to us as if the decay products simply popped into existence with an accompanying realease of energy.
Maybe I wasn't clear. Direct detection of LSP may be some time away, but given the flux density of this proposed DM candidate, should we not have seen (serendipitously) the spontaneous production of the decay products of the LSP in at least some accelerator detectors by now?
Well, the LSP cannot decay, but I suppose what you mean is annihilation products produced by collisions between LSP's.
Think of this: Interactions between WIMPs and ordinary matter in the direct detection experiments are not frequent enough to be detected. The density of ordinary matter in a detector is way higher than the expected local WIMP density. Which event should occur more often: WIMPs interacting with the detector, or WIMPs interacting with WIMPs? What conclusion can be drawn?
turbo-1
Mar13-06, 07:30 PM
From what I have read (and I will qualify this by saying that I have a physical revulsion to tacking over a hundred new dimensionless parameters on the standard model to extend it with MSSM, so I have not been a real fan of any brand of SUSY) LSPs (in pairs) can decay in pairs into lighter baryonic particles plus gamma rays. Given the predicted flux of LSPs, shouldn't we have observed at least one such decay by now? If not, why not? Indirect detections of LSP seem a whole lot more likely than direct detections.
From what I have read (and I will qualify this by saying that I have a physical revulsion to tacking over a hundred new dimensionless parameters on the standard model to extend it with MSSM, so I have not been a real fan of any brand of SUSY) LSPs (in pairs) can decay in pairs into lighter baryonic particles plus gamma rays.
When two particles interact and annihilate into something new, we usually don't call it a "decay". "Decay" is something a single particle does. That's why I objected to your use of the word. But anyway...
Given the predicted flux of LSPs, shouldn't we have observed at least one such decay by now? If not, why not? Indirect detections of LSP seem a whole lot more likely than direct detections.
I'll repeat:
Think of this: Interactions between WIMPs and ordinary matter in the direct detection experiments are not frequent enough to be detected. The density of ordinary matter in a detector is way higher than the expected local WIMP density. Which event should occur more often: WIMPs interacting with the detector, or WIMPs interacting with WIMPs?What conclusion can be drawn?
turbo-1
Mar14-06, 02:10 PM
Thanks for the clarification on the use of decay products vs aniihilation products. Do you know of a paper that lays out an estimate for the WIMP annihilation rate (perhaps as a percentage of total flux)? I have not been able to find one.
SpaceTiger
Mar14-06, 02:57 PM
Thanks for the clarification on the use of decay products vs aniihilation products. Do you know of a paper that lays out an estimate for the WIMP annihilation rate (perhaps as a percentage of total flux)? I have not been able to find one.
Here's an estimate based on an excess of microwave emission near the center of the galaxy:
Finkbeiner 2004 (http://arxiv.org/pdf/astro-ph/0409027)
turbo-1
Mar15-06, 11:54 AM
Thank you for the link, ST. I have done a little searching to determine detector volumes and found the dimensions of a "drift chamber" that is 26cm radius with a 16cm radis core through which the beam runs, and a chamber length of 2m. The detector has a radial cross section of about 1318cm2 and a total volume of 263,600 cm3.
Assuming a flux of 6x104 WIMPs /s/cm2 (from the paper I linked previously) and a longitudinal detector cross/section of 5200cm2, there should be 3.12x108 WIMPS traversing the detector every second. Shouldn't we have seen at least one WIMP annihilation event in all the years particle accelerators/colliders have been in operation?
Chronos
Mar16-06, 02:31 AM
I assume you have some statistics in mind.
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