Favorite DM particle

  1. wolram

    wolram 3,730
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    http://arxiv.org/pdf/astro-ph/0403064
    This is a 2004 paper 34 pages on dark matter, various candidates for
    DM are discussed and categorised
    anyone have a favorite DM particle?.
     
  2. jcsd
  3. Garth

    Garth 3,418
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    Thank you for the link to Gondolo’s paper, we have quite a choice as to our favourite particle. I quote from it:

    He continues,
    He concludes:
    Quite

    But consider; in Gondolo’s paper Figure 1 on page 2 is the well-known concordance Omega m v Omega lambda diagram. The total Omega is thought to be unity because the WMAP data favours a flat universe; this constrains Omega lambda as the total is thought therefore to be unity.

    However other models are also conformally flat, such as SCC which is so - even with a total Omega of only one third. If you notice putting Omega m = 0.33, and therefore the equivalent Omega lambda = 0.66, fits quite well too, in fact it is dead centre of the intersection of the CMB and distant supernovae data sets.

    Furthermore the Omega baryonic matter in SCC is 0.22, (effective Omega lambda still 0.66), which is the centre of the Galaxy red shift survey data set.

    So one way of understanding the different data sets plotted on that diagram is to say the CMB and distant supernovae data indicate cosmological dynamics determined by the total density whereas the galaxy survey data indicate the dynamics of galaxies and clusters within the universe determined by the baryonic matter, dark and luminous, within those clusters.

    Just food for thought.

    My favourite dark matter particle is the proton, closely followed by the electron and neutron!

    Garth
     
    Last edited: Sep 30, 2004
  4. selfAdjoint

    selfAdjoint 8,147
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    Garth, conformally flat is different from flat!
     
  5. Garth

    Garth 3,418
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    True, but conformal transformations preserve angles. The CMB data is based on the angular size of anisotropies in the radiation. The conclusions drawn carry through to conformal transformations of the particular GR model.
    Garth
     
  6. I vote for the axion, a WIMP whose mass must be in the range 10-6-10-3 eV. The axion is in the category of cold dark matter. I used to have preference for hot dark matter (exemple, the neutrino), but WMAP result indicates that the missing matter is most likely cold dark matter
    There's a theory that proposes that the axion could act as dark energy as well. Is called Axion Phantom energy
    http://arxiv.org/abs/hep-th/0401082
     
    Last edited: Sep 30, 2004
  7. wolram

    wolram 3,730
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    http://www.astro.umd.edu/~ssm/mond/
    Garth, Meteor, do you have a view on how these particles arrange
    themselves with galaxies?
    The url is a link to the mond pages, as you know an alternative to DM.
    Although i do not subscribe to the theory it is a good one stop reference.
     
  8. Garth

    Garth 3,418
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    MOND would be more persuasive if the mechanism that produces the anomalous acceleration was known.

    SCC predicts the density of the universe is 2/3 baryonic and 1/3 false vacuum energy. Models already run on such a constitution in the past (2/3 CDM, 1/3 HDM) modelled galaxy formation quite nicely
    Garth
     
  9. Wolram,
    dark matter is postulated to exist throughout all the universe, not only in galaxies, but also in the intergalactic medium. In disk galaxies for example, they exist in the disk but also in a spherical volume around the disk called the halo. The most widely accepted model for dark matter in halos is the famous NFW profile (Navarro, Frenk, White, 1996). It seems that the ratio of dark matter to visible matter varies according what scale of the universe are you examining. See

    http://hermes.physics.ox.ac.uk/users/Astrophysics/guides/galaxies/dkmatter.shtml

    "Within galaxies the amount of dark matter appears to exceed the amount of visible matter by a factor of 10 to 1 in some cases, and even more than this for a few galaxies. Within galaxy clusters the ratio of dark to visible matter appears to be even larger still and a general result is that the ratio of dark to visible matter appears to increase as one observes on larger scales. On the very largest scales of all (the scale of the observable Universe) visible matter may account for less than 1% of all the matter in the Universe."
     
  10. Dark Dimension

    This might go better in String theory, but couldn't dark matter be a fundamental 'particle' that exists in other dimensions? If all particles are vibrations of a fundamental string, then there's nothing that says there can't be particles that vibrate higher than light. But as speed of light is the measure for our space-time, we wouldn't never detect it inside our space-time. It might be curled up in compact dimensions because of it's FLT vibratory nature. Yet its effects might be inferred, such as through gravitational influence.

    Hey, it's as good as made-up particles with ultraweak interactions.
     
  11. Last edited: Oct 2, 2004
  12. Nereid

    Nereid 4,014
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    I keep promising - to myself - to investigate the data on primordial abundances, observational data on low metalicity stars, Lyman forest work, and so on, to get a richer picture of how well these constrain (rule out?) SCC (the 'Indian team's paper' says nothing useful, unless I've been reading the wrong paper).

    As we've discussed before, simply substituting baryonic DM for non-baryonic DM in a cosmological model doesn't get you very far ... the distribution of DM is, in some cases, very well known, so an alternative cosmological model still has plenty of good DM data to get its teeth into. For example, does SCC have a hierarchical approach to galaxy formation? In SCC, what sort of DM would comprise the DM in galaxy halos? If it's baryonic matter, why hasn't it been detected yet (e.g. through footprints in the misnamed galactic cosmic rays, in starbursts resulting from galaxy collisions, in microlensing searches, ...)?

    A completely different question: other than SCC, what alternative ('non-standard') cosmological models do away with non-baryonic DM? Please, only those with a reasonable degree of concordance with good observational results.
     
    Last edited: Oct 2, 2004
  13. Garth

    Garth 3,418
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    Try:
    D.Lohiya, A. Batra, S. Mahajan, A. Mukherjee, http://arxiv.org/abs/nucl-th/ 9902022 ;
    Phys. Rev. D60, 108301 (2000).

    Annu: A. Batra, D. Lohiya, S. Mahajan, A. Mukherjee, Int. J. Mod.
    Physics D10, 1 (2001).

    Batra, A., Lohiya, D., Mahajan, S., & Mukherjee, A. 2000, Int. J. Mod. Phys., D9,757;

    Batra, A., Sethi, M., & Lohiya, D. 1999, Phys. Rev. D., 60, 108301.

    G. Steigman http://arxiv.org/abs/astro-ph/9601126 , (1996) is interesting too!
    good questions applicable to both LCDM and SCC models
    MOND?
    Garth
     
  14. Nereid

    Nereid 4,014
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    Thanks.
    You are, no doubt, aware of the LCDM 'answers'!
    Not AFAIK! MOND's domain of applicability is limited; it certainly does not claim to be universal. In fact, being inconsistent with GR, it's hard to imagine how it could be modified to make it applicable.
     
  15. Garth

    Garth 3,418
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    Yes - to invent Dark Matter and Energy!
    I quote again from Gondolo's paper:
    (Emphasis mine)

    Garth
     
    Last edited: Oct 3, 2004
  16. Garth

    Garth 3,418
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    There was this paper: Stacy McGaugh http://arxiv.org/abs/astro-ph/0312570
    "Confrontation of MOND Predictions with WMAP First Year Data"
    although that required a heavy neutrino (1eV), which seems to have been ruled out now.
    Although I do not advocate MOND myself, I find its lack of identifying a mechanism to explain the anomalous MOND acceleration no more disqualifying that the standard theory's lack of identifying DM particle and DE to explain its dynamics.

    Garth
     
  17. turbo

    turbo 7,366
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    How true! In this article:

    http://www.esa.int/esaCP/SEME3PXO4HD_FeatureWeek_0.html

    the authors explain how dark matter aligns itself very closely with the galaxies in the cluster. They propose no mechanism, and there is no observable effect from the dark matter other than the overly-strong lensing. It is perhaps too easy to measure the errors (as evidenced by excess lensing) in the standard model and attribute them to DM, and even make maps of the distribution of this mysterious stuff.

    Garth, I know that you prefer baryonic matter as DM, but what kind of baryonic matter could comprise 90-95% of the cluster mass and have NO thermal signature? (Again, IIR, you propose a much smaller percentage of DM - somewhat on the order of 30%, correct?)

    I firmly believe that we will find the zero point energy field to be the real player in this regard. Just a tiny difference in infall rates (matter vs anti-matter) could polarize the ZPE EM field in the presence of huge masses, and that polarization should affect the optical properties of space-time. The breaking of this equivalence (matter/antimatter gravitational infall rates) would also provide a mechanism for giving us a matter-dominated universe, in accordance with Smolin's black-hole universe ideas.

    The potential energy of the ZPE field is over 120 orders of magnitude too high to account for the cosmological constant, but what if that energy cannot be expressed if the field is randomly oriented? Polarization due to the presence of mass could express some of this energy, even if the infall rates of matter vs antimatter differ by a small amount. Just a thought...
     
    Last edited: Oct 3, 2004
  18. Garth

    Garth 3,418
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    That may be so, but what property of anti-matter would cause it to respond to a gravitational field differently from ordinary matter?

    SCC simply takes the Brans Dicke theory, which modifies GR by including a scalar field to fully include Mach's Principle, and modifies it by allowing that field to interact with matter to include the local conservation of energy. We then have a theory that satisfies present experimental tests of the EP, solar system tests of GR and a cosmology that is conformally flat, strictly linearly expansion with a total density, (densities as a proportion of critical density) of 33% of which 11% is ZPE determined by the field equations. Of the remaining 22%, about 20% is baryonic and 1 or 2 % unaccounted for, possibly a neutrino component.
    Before WMAP decreed the universe was flat and therefore of 100% density the density of the universe was generally thought to be about a third, luminous density 2%, DM for clusters 20%. ("Inflation is dead, Long live inflation", Scientific American, Science and the Citizen, July 1998 pg. 9) which fits remarkably well with the un-massaged predictions of SCC; that is if the 2% is allow to enlarge to absorb the 20% because of freely coasting nucleo-synthesis.

    I do acknowledge the problem of identifying what form the baryonic DM takes, I haven't solved all the problems at once there are some still to chew over!!

    I am interested in the weak lensing and cluster dynamics results that may be obtained if the assumption is not made that Omega-total = 1, because the WMAP apparent flatness may be explained by conformal geometry.

    Garth
     
    Last edited: Oct 3, 2004
  19. Garth

    Garth 3,418
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    Is it true that the DM has no signature? How dense is the IGM that produces the Lyman alpha forest? Could this be the signature of cold (~3K) gas and metals in the intergalactic voids?

    Garth
     
  20. turbo

    turbo 7,366
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    I'm sure my CiteBase procedure has holes in it (there is TOO MUCH to read!), but so far, I've not seen any signature of CDM cited in the literature, apart from refraction. No cited absorption, diffusion, nor spectral dispersion. CDM can't be matter, unless it the least interactive matter imaginable. ZPE fields, anyone?
     
  21. Chronos

    Chronos 9,859
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