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Can the Li7 problem be resolved by increasing the dark matter ratio?

  1. Sep 27, 2010 #1


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    Currently the WMAP results give a baryon:photon ratio of ~6.2x10-10, and a dark:baryonic mass ratio of ~5. When added to the energy density of photons + neutrinos (+dark energy at later times), the total density is then critical for a flat Universe. The BB nucleosynthesis analysis of the relative abundance of 4He, D, 3He, and 7Li strongly suggest that the baryon:photon ratio is <4.5x10-10 with 4-5 sigmas confidence level (excluding some kind of likely systematic error in 7Li) See figs 3 and 4 of


    If the dark:baryonic mass ratio remains ~5, and we believe the 7Li results, this would put the energy density at the CMB last scattering surface at only ~79% of critical. Can this be fixed simply by increasing the dark:baryonic mass ratio, or is there some independent reason the ratio must be 5?
    Last edited: Sep 27, 2010
  2. jcsd
  3. Sep 28, 2010 #2


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    WMAP already constrains the baryon/dark matter ratio incredibly tightly. You just can't change that ratio much without altering the power spectrum of the CMB far outside of WMAP's measurement errors.

    What this may be telling us, however, is something interesting about the temperature of the dark matter. If the dark matter has some non-zero temperature, it may potentially have some impact on BBN. However, I strongly suspect that the real answer lies in stellar physics, not in BBN.
  4. Sep 29, 2010 #3
    Same here. My first guess would be that the Li-7 was burned up by Pop III stars. (What pop III stars? Well the same one's that magically produced the heavy elements in quasars.)

    It's easier to burn up light elements than to produce them.
  5. Sep 29, 2010 #4


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    I sympathize with Twofish. There is a lot about pop III stars we do not have a handle on [not to mention stellar processes in general]. Obviously, the early universe was more heavily polluted by metallicity than expected by theory.
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