4.6. Testing The Consistency Of SBBN

As impressive as is the agreement among the three independent estimates of the universal baryon density, we should not be lured into complacency. The apparent success of SBBN should impell us to test the standard model even further. How else to expose possible systematic errors which have heretofore been hidden from view or, to find the path beyond the standard models of cosmology and particle physics? To this end, in Figure 13 are compared the SBBN ⁴He (Y) and D (D/H) abundance predictions along with the estimates for Y and D/H adopted here. The agreement is not very good. Indeed, while for ₁₀ = 5.8_-0.6^+0.4, (D/H)_SBBN = 2.8_-0.7^+0.4 × 10^-5, in excellent agreement with the O'Meara et al. (2001) estimate, the corresponding ⁴He abundance is predicted to be Y_SBBN = 0.248 ± 0.001, which is 2 above our OSW-adopted primordial abundance. Indeed, the SBBN-predicted ⁴He abundance based directly on deuterium is also 2 above the IT/ITL estimate. Here is a potential challenge to the internal consistency of SBBN. Given that systematic errors dominate, it is difficult to decide how seriously to take this challenge. In fact, if ⁴He and D, in concert with SBBN, are each employed as baryometers, their likelihood distributions for are consistent at the 7% level.

Figure 13. The diagonal band is the SBBN-predicted helium-4 mass fraction versus the SBBN-predicted deuterium abundance (by number relative to hydrogen). The width of the band accounts for the theoretical uncertainties in the SBBN predictions. Also shown by the filled circle and error bars are the primordial 4He and D abundance estimates adopted here.

An apparent success of (or, a potential challenge to) SBBN emerges from a comparison between D and ⁷Li. In Figure 14 is shown the SBBN-predicted relation between primordial D and primordial ⁷Li along with the relic abundance estimates adopted here (Pinsonneault et al. 2002). Also shown for comparison is the Ryan et al. (2000) primordial lithium abundance estimate. The higher, depletion/dilution-corrected lithium abundance of PSWN is in excellent agreement with the SBBN-D abundance, while the lower, RBOFN value poses a challenge to SBBN.

Figure 14. The band is the SBBN-predicted lithium abundance (by number relative to hydrogen) versus the SBBN-predicted deuterium abundance. The width of the band accounts for the theoretical uncertainties in the SBBN predictions. Also shown is the Pinsonneault et al. (2002; PSWN) primordial lithium abundance estimate adopted here (filled triangle) along with the Ryan et al. (2000; RBOFN) estimate (filled circle).