Updated Big Bang Nucleosynthesis confronted to WMAP observations and to the Abundance of Light Elements

TL;DR

This paper updates Standard Big-Bang Nucleosynthesis (SBBN) calculations by incorporating the Descouvemont et al. (2003) nuclear input with a Monte-Carlo treatment of reaction-rate uncertainties. It demonstrates that the resulting deuterium abundances align well with WMAP-derived baryon densities and high-redshift D/H measurements, reinforcing the cosmological value of $\Omega_b h^2$. However, a robust lithium-7 discrepancy remains between SBBN+WMAP predictions and halo-star observations, prompting discussion of observational systematics, stellar depletion, or new nuclear pathways—particularly Be-7 destruction channels—that could reconcile the results. The study underscores the need for precise nuclear data and targeted experiments to determine whether nuclear physics can resolve the lithium problem or if new physics must be invoked. Overall, the work strengthens the concordance between BBN and CMB constraints for D/H while highlighting lithium as the key tension demanding further investigation.

Abstract

We improve Standard Big Bang Nucleosynthesis (SBBN) calculations taking into account new nuclear physics analyses (Descouvemont et al. 2003). Using a Monte-Carlo technique, we calculate the abundances of light nuclei versus the baryon to photon ratio.The results concerning omegab are compared to relevant astrophysical and cosmological observations. Consistency between WMAP, SBBN results and D/H data strengthens the deduced baryon density and has interesting consequences on cosmic chemical evolution. A significant discrepancy between the calculated Li-7 deduced from WMAP and the Spite plateau is clearly revealed. To explain this discrepancy three possibilities are invoked : uncertainties on the Li abundance, surface alteration of Li in the course of stellar evolution or poor knowledge of the reaction rates related to Be-7 destruction. In particular, the possible role of the up to now neglected Be-7(d,p)2He-4 and Be-7(d,alpha)Li5 reactions is considered. The impressive advances in CMB observations provide a strong motivation for more efforts in experimental nuclear physics and high quality spectroscopy to keep BBN in pace.

Figures (5)

• Figure 1: Abundances of $^4He$ (mass fraction), $D$, $^3He$ and $^{7}Li$ (by number relative to H) as a function of the baryon over photon ratio $\eta$ or $\Omega_bh^2$ . Limits (1-$\sigma$) are obtained from Monte Carlo calculations. Hatched area represent primordial $^4He$, $D$ and $^{7}Li$ abundances deduced from different primitive astrophysical sites (see Section \ref{['s:obs']}): Izotov et al. (1999) (high area) and Luridiana et al. (2003) (low area) for $^4He$, Kirkman et al. (2003) for $D$, and Ryan et al. (2000) for $^{7}Li$ (95% c.l.). Concerning $^{7}Li$, we also show an upper limit derived from Bonifacio et al. (2002) observations (dashed line). The vertical stripe represents the (1-$\sigma$) $\Omega_bh^2$ limits provided by WMAP (Spergel et al. 2003).
• Figure 2: Observed abundances as a function of metallicity from objects which are expected to reflect primordial abundances. Upper panel : observed $D$ abundances in cosmological clouds (parenthesis indicate less established observations.) The mean observational value (Kirkman et al. 2003) and the highest observed value used in CV are shown by arrows. The horizontal stripe represents the (1-$\sigma)$$\Omega_bh^2$ limits provided by WMAP+BBN. Lower panel : observed $^{7}Li$ abundances from Ryan et al. (1999; 2000) and extrapolated primordial abundance Ryan et al. (2000) shown by an arrow. $Li/H$ observations in a globular cluster at [Fe/H]=-2 ( Thévenin et al. 2001; Bonifacio et al. 2002) are also displayed. The horizontal stripe represents the (1-$\sigma)$$\Omega_bh^2$ limits provided by WMAP+BBN.
• Figure 3: The 12 main SBBN reactions plus $^7$Be(d,p)2$^4$He.
• Figure 4: Same as Figure \ref{['f:heli']}, lower panel, but including the effect of $^7$Be(d,p)2$^4$He rate variations while other reaction rates are set to their nominal values. The solid curve is the reference where the $^7$Be(d,p)2$^4$He rate from CF88 is used, while the dash--dotted curves correspond to an increase of the rate by factors of 30, 100, 300 and 1000.
• Figure 5: The only experimental data available for the $^7$Be(d,p)2$^4$H reaction from Kavanagh (1960). The displayed $S$--factor is calculated as in Parker (1972) from the differential cross section at 90$^\circ$ ($\times4\pi$) leading to the ground and first $^8$Be excited states. Note that no data is available at SBBN energies as shown by the Gamow peaks for T$_9$ = 1 and 0.5.