Solar neutrino constraints on the BBN production of Li

Abstract

Using the recent WMAP determination of the baryon-to-photon ratio, 10 10 ϭ6.14 to within a few percent, big bang nucleosynthesis ͑BBN͒ calculations can make relatively accurate predictions of the abundances of the light element isotopes which can be tested against observational abundance determinations. At this value of , the 7 Li abundance is predicted to be significantly higher than that observed in low metallicity halo dwarf stars. Among the possible resolutions to this discrepancy are ͑1͒ 7 Li depletion in the atmosphere of stars, ͑2͒ systematic errors originating from the choice of stellar parameters-most notably the surface temperature, and ͑3͒ systematic errors in the nuclear cross sections used in the nucleosynthesis calculations. Here, we explore the last possibility, and focus on possible systematic errors in the 3 He(␣,␥) 7 Be reaction, which is the only important 7 Li production channel in BBN. The absolute value of the cross section for this key reaction is known relatively poorly both experimentally and theoretically. The agreement between the standard solar model and solar neutrino data thus provides additional constraints on variations in the cross section (S 34 ). Using the standard solar model of Bahcall, and recent solar neutrino data, we can exclude systematic S 34 variations of the magnitude needed to resolve the BBN 7 Li problem at the տ95% C.L., or more strongly, depending on the Li observations used. Additional laboratory data on 3 He(␣,␥) 7 Be will sharpen our understanding of both BBN and solar neutrinos, particularly if care is taken in determining the absolute cross section and its uncertainties. Nevertheless, it is already clear that this ''nuclear fix'' to the 7 Li BBN problem is unlikely; other possible solutions are briefly discussed.

The effects of He I λ10830 on helium abundance determinations

“…The most recent Planck result [4] for the baryon density, Ω B h 2 = 0.02226 ± 0.00016, corresponds to a baryon-to-photon ratio of η = (6.10 ± 0.04) × 10 −10 . Because the uncertainty in η is now less than 1%, standard big bang nucleosynthesis (SBBN) [5][6][7] is a parameter-free theory [8], and relatively precise predictions of the primordial abundances of the light elements D, 3 He, 4 He, and 7 Li are available [9][10][11][12][13][14][15][16][17][18][19][20][21][22]. While the 7 Li abundance remains problematic [17], recent D/H determinations from quasar absorption systems have become quite precise, in their own right, and they are in excellent agreement with the prediction from SBBN and the CMB [23].…”

Did something decay, evaporate, or annihilate during big bang nucleosynthesis?

“…The predicted 7 Li should be compared to the observationally inferred primordial 7 Li/H= 1.23 +0.34 −0.16 × 10 −10 [10] abundance from the inferred 7 Li in atmospheres of extreme Pop II stars belonging to the Spite plateau (where the analysis corrects for 7 Li production by cosmic rays), or to the inferred 7 Li = 2.19 +0.30 −0.27 × 10 −10 [11] from low-metallicity stars within the globular cluster NGC 6397, indicating if taken at face value, that there may be a problem in SBBN. This discrepancy may not be resolved by nuclear reaction rate uncertainties in the main lithium-producing reaction 3 He(α, γ) 7 Be [7] and only very unlikely due to uncertainties in the lithium-destroying reaction 7 Be(d, p)2 4 He [8]. It is conceivable, however, that it is due to other systematic uncertainties entering the inference of primordial 7 Li abundances, such as stellar astration of 7 Li in lowmetallicity stars, or imprecise determinations of stellar surface temperatures in these stars.…”

“…30 −0.27 × 10 −10 [11] from low-metallicity stars within the globular cluster NGC 6397, indicating if taken at face value, that there may be a problem in SBBN. This discrepancy may not be resolved by nuclear reaction rate uncertainties in the main lithium-producing reaction 3 He(α, γ) 7 Be [7] and only very unlikely due to uncertainties in the lithium-destroying reaction 7 Be(d, p)2 4 He [8]. It is conceivable, however, that it is due to other systematic uncertainties entering the inference of primordial 7 Li abundances, such as stellar astration of 7 Li in lowmetallicity stars, or imprecise determinations of stellar surface temperatures in these stars.…”

“…Furthermore an independent determination of the fractional contribution of baryons to the critical density, Ω b , from precision measurements of the cosmic microwave background radiation (CMB) by various balloon missions and the WMAP [2] sattelite has become feasible. These observations together with the ever-continuing observational and theoretical efforts to deduce precise primordial 4 He/H-and 7 Li/H-ratios, leave BBN in an essentially observationally overconstrained state, opening the possibility to question internal consistency of the predictions of SBBN. If such a check is performed it shows that SBBN is to first approximation internally consistent, though inconsistencies or tensions between predicted-and observationally inferredabundances may exist at higher order.…”

“…The predicted 7 Li should be compared to the observationally inferred primordial 7 Li/H= 1.23 +0. 34 −0.16 × 10 −10 [10] abundance from the inferred 7 Li in atmospheres of extreme Pop II stars belonging to the Spite plateau (where the analysis corrects for 7 Li production by cosmic rays), or to the inferred 7 Li = 2.19 +0. 30 −0.27 × 10 −10 [11] from low-metallicity stars within the globular cluster NGC 6397, indicating if taken at face value, that there may be a problem in SBBN.…”