Present status of primordial nucleosynthesis after WMAP: results from a new BBN code

TL;DR

This paper presents a revised Big Bang Nucleosynthesis (BBN) framework that integrates a comprehensive update of nuclear reaction rates with a numerically stable BBN code, enabling precise predictions for light-element abundances. By combining a new BBN code with NACRE-based rates and refined weak interaction inputs, the authors perform joint likelihood analyses with WMAP-derived $oldsymbol{ω_b}$ and Deuterium observations to test the standard BBN scenario and constrain the effective number of relativistic species $oldsymbol{N_{eff}}$ and potential neutrino degeneracies $oldsymbol{ξ_e}$. The results show Deuterium abundances are consistent with a three-neutrino, standard model across CMB and BBN, while $^4He$ hints at possible systematics or a small departure from the standard picture; including $oldsymbol{ξ_e}$ in degenerate BBN can alleviate some tensions but broadens the allowed parameter space for extra relativistic species. Overall, the work tightens theoretical uncertainties in D and $^4He$ predictions, underscores the need for improved $^4He$ measurements, and demonstrates that current data are broadly compatible with a standard BBN framework, albeit with room for new physics if future observations tighten the constraints on $N_{eff}$ and lepton asymmetries.

Abstract

We report on the status of primordial nucleosynthesis in light of recent results on CMB anisotropies from WMAP experiment. Theoretical estimates for nuclei abundances, along with the corresponding uncertainties, are evaluated using a new numerical code, where all nuclear rates usually considered have been updated using the most recent available data. Moreover, additional processes, neglected in previous calculations, have been included. The combined analysis of CMB and primordial nucleosynthesis prediction for Deuterium gives an effective number of relativistic degrees of freedom in good agreement with the simplest scenario of three non degenerate neutrinos. Our findings seem to point out possible systematics affecting 4He mass fraction measurements, or the effect of exotic physics, like a slightly degenerate relic neutrino background.

Figures (10)

• Figure 2: The 68 and 95% C.L. likelihood contours from WMAP data in the $N_{eff}-\omega_b$ plane.
• Figure 3: The marginalized likelihoods versus $N_{eff}$ and $\omega_b$.
• Figure 4: Arbitrary levels of the bidimensional marginalized likelihood contours: $x$-axis in first (second) column corresponds to $N_{eff}$ ($\omega_b$), from top to bottom $y$-axis corresponds to $\omega_b$, $\omega_c$, $h$, $\tau$ and $n_s$, respectively.
• Figure 5: The pulls (see text) of QSO D measurements with respect to the theoretical prediction for $N_{eff}=3.01$ and $\omega_b=0.023$, in units of $\left((\sigma^{th}_{22})^2 + (\sigma^{exp}_2)^2 \right)^{1/2}$.
• Figure 6: Left plot: the $68$ and $95\%$ C.L. contours in the $\omega_b-N_{eff}$ plane for WMAP (solid lines). The dashed lines are two arbitrary levels of the BBN Deuterium likelihood. The joint $95\%$ C.L. $CMB+BBN$ region is shown as the filled area. Right plot: the joint $95\%$ C.L. contour of the left plot (solid line) is compared to the same contour with a total error on $X_D$ improved by a factor 2 (filled area).