New reaction rates for improved primordialD/Hcalculation and the cosmic evolution of deuterium

Abstract

Primordial or big bang nucleosynthesis (BBN) is one of the three historical strong evidences for the big bang model. Standard BBN is now a parameter free theory, since the baryonic density of the Universe has been deduced with an unprecedented precision from observations of the anisotropies of the cosmic microwave background (CMB) radiation. There is a good agreement between the primordial abundances of 4 He, D, 3 He and 7 Li deduced from observations and from primordial nucleosynthesis calculations. However, the 7 Li calculated abundance is significantly higher than the one deduced from spectroscopic observations and remains an open problem. In addition, recent deuterium observations have drastically reduced the uncertainty on D/H, to reach a value of 1.6%. It needs to be matched by BBN predictions whose precision is now limited by thermonuclear reaction rate uncertainties. This is especially important as many attempts to reconcile Li observations with models lead to an increased D prediction. Here, we re-evaluates the d(p,γ) 3 He, d(d,n) 3 He and d (d,p) 3 H reaction rates that govern deuterium destruction, incorporating new experimental data and carefully accounting for systematic uncertainties. Contrary to previous evaluations, we use theoretical ab initio models for the energy dependence of the S-factors. As a result, these rates increase at BBN temperatures, leading to a reduced value of D/H = (2.45±0.10) × 10 −5 (2σ), in agreement with observations.

Primordial Nucleosynthesis

“…In our latest work [5], we adopted for the baryon-to-photon ratio, the constraints obtained with the largest set of CMB data (TT,TE,EE+lowP), without any external data, giving Ω b ·h 2 = 0.02225±0.00016, together with N ν =3 for the number of neutrino families and τ n = 880.3±1.1 s [6] for the neutron lifetime. The nuclear reaction rates are those listed in [7] with only a few updates listed below.…”

“…An improved evaluation of the 3 He(α, γ) 7 Be reaction rate has been published [8], using a Monte-Carlo based R-matrix analysis. The effect of these re-evaluations can be seen between columns 2 and 3 in Table I, while columns 4 shows the effect of the re-evaluated reaction rates [5] for deuterium destruction (see § 3). Column 5 represent the results of a Monte Carlo calculation [5] as described in [7,9] but with these few new rates, to be compared with observations in Column 6.…”

“…Column 5 represent the results of a Monte Carlo calculation [5] as described in [7,9] but with these few new rates, to be compared with observations in Column 6. [5].…”

“…These extra neutrons, inevitably, also boost the D and 3 H production through the 1 H(n,γ) 2 H and 3 He(n,p) 3 H channels, respectively [17]. The dashed curve [5] represent an approximation [Eq. 7.4 in [5]] of the interplay between Li/H and D/H when neutrons are injected towards the end of BBN (T <0.5 GK).…”

“…The dashed curve [5] represent an approximation [Eq. 7.4 in [5]] of the interplay between Li/H and D/H when neutrons are injected towards the end of BBN (T <0.5 GK). In this approximation, the flow through the 3 He(n,p) 3 H reaction is neglected but it shows up in the lower limit (≈ 0.6 × 10 −10 in Fig.…”