International Journal of Modern Physics E

Primordial nucleosynthesis remains as one of the pillars of modern cosmology. It is the testing ground upon which many cosmological models must ultimately rest. It is our only probe of the universe during the important radiation-dominated epoch in the first few minutes of cosmic expansion. This paper reviews the basic equations of space-time, cosmology, and big bang nucleosynthesis. We also summarize the current state of observational constraints on primordial abundances along with the key nuclear reactions and their uncertainties. We summarize which nuclear measurements are most crucial during the big bang. We also review various cosmological models and their constraints. In particular, we analyze the constraints that big bang nucleosynthesis places upon the possible time variation of fundamental constants, along with constraints on the nature and origin of dark matter and dark energy, long-lived supersymmetric particles, gravity waves, and the primordial magnetic field.

Primordial nucleosynthesis, or big bang nucleosynthesis (BBN), is one of the three evidences for the big bang model, together with the expansion of the universe and the cosmic microwave background. There is a good global agreement over a range of nine orders of magnitude between abundances of ⁴He, D, ³He and ⁷Li deduced from observations, and calculated in primordial nucleosynthesis. However, there remains a yet-unexplained discrepancy of a factor $\approx 3$, between the calculated and observed lithium primordial abundances, that has not been reduced, neither by recent nuclear physics experiments, nor by new observations. The precision in deuterium observations in cosmological clouds has recently improved dramatically, so that nuclear cross-sections involved in deuterium BBN needs to be known with similar precision. We will briefly discuss nuclear aspects related to the BBN of Li and D, BBN with nonstandard neutron sources, and finally, improved sensitivity studies using a Monte Carlo method that can be used in other sites of nucleosynthesis.

We review the recent progress in the Big-Bang nucleosynthesis which includes the standard and nonstandard theory of cosmology, effects of neutrino degeneracy, and inhomogeneous nucleosynthesis within the framework of a Friedmann model. As for a nonstandard theory of gravitation, we adopt a Brans–Dicke theory which incorporates a cosmological constant. We constrain various parameters associated with each subject.

We review important reactions in the Big Bang Nucleosynthesis (BBN) model involving a long-lived negatively charged massive particle, $X^{-}$, which is much heavier than nucleons. This model can explain the observed ⁷Li abundances of metal-poor stars, and predicts a primordial ⁹Be abundance that is larger than the standard BBN prediction. In the BBN epoch, nuclei recombine with the $X^{-}$ particle. Because of the heavy $X^{-}$ mass, the atomic size of bound states $A_X$ is as small as the nuclear size. The nonresonant recombination rates are then dominated by the $D$-wave $\to 2P$ transition for ⁷Li and ${}^{7,9}$Be. The ⁷Be destruction occurs via a recombination with the $X^{-}$ followed by a proton capture, and the primordial ⁷Li abundance is reduced. Also, the ⁹Be production occurs via the recombination of ⁷Li and $X^{-}$ followed by deuteron capture. The initial abundance and the lifetime of the $X^{-}$ particles are constrained from a BBN reaction network calculation. We derived parameter region for the ⁷Li reduction allowed in supersymmetric or Kaluza–Klein (KK) models. We find that either the selectron, smuon, KK electron or KK muon could be candidates for the $X^{-}$ with $m_X\sim {𝒪}(1)$ TeV, while the stau and KK tau cannot.

We review a nonstandard Big-Bang Nucleosynthesis (BBN) scenario within the minimal supersymmetric standard model, and propose an idea to solve both the ${}^7\text{Li}$ and ${}^6\text{Li}$ problems. Each problem is a discrepancy between the predicted abundance in the standard BBN and observed one. We focus on the stau, a supersymmetric partner of tau lepton, which is a long-lived charged particle when it is the next lightest supersymmetric particle and is degenerate in mass with the lightest supersymmetric particle. The long-lived stau forms a bound state with a nucleus, and provides nonstandard nuclear reactions. One of those, the internal conversion process, accelerates the destruction of ${}^7\text{Be}$ and ${}^7\text{Li}$, and leads to a solution to the ${}^7\text{Li}$ problem. On the other hand, the bound state of the stau and ${}^4\text{He}$ enhances productions of n, D, T and ${}^6\text{Li}$. The over-production of ${}^6\text{Li}$ could solve the ${}^6\text{Li}$ problem; while the over-productions of D and T could conflict with observations, and hence the relevant parameter space of the stau is strictly constrained. We therefore need to carefully investigate the stau–${}^4\text{He}$ bound state to find a condition of solving the ${}^6\text{Li}$ problem. The scenario of the long-lived stau simultaneously and successfully fits the abundances of light elements (D, T, ${}^3\text{He}$, ${}^4\text{He}$, ${}^6\text{Li}$ and ${}^7\text{Li}$) and the neutralino dark matter to the observed ones. Consequently, the parameter space both of the stau and the neutralino is determined with excellent accuracy.

The Big Bang Nucleosynthesis theory accurately reproduces the abundances of light elements in the universes, except for the ⁷Li abundance. The calculated ⁷Li abundance with the baryon-to-photon ratio fixed by the observations of the cosmic microwave background (CMB) is inconsistent with the observed lithium abundances on the surface of metal-poor halo stars, and this problem is called “⁷Li problem”. Previous studies proposed to resolve this ⁷Li problem include photon cooling (possibly via the Bose–Einstein condensation of a scalar particle), the decay of a long-lived $X$ particle (possibly the next-to-lightest supersymmetric particle), or an energy density of a primordial magnetic field (PMF). We review and analyze the results of these solutions both separately and in concert, and the constraint on the $X$ particles and the PMF parameters from observed light-element abundances with a likelihood analysis. We can discover parameter ranges of the $X$ particles which can solve the ⁷Li problem and constrain the energy density of the PMF.

The term dark radiation is used both to describe a noninteracting neutrino species and as a correction to the Friedmann Equation in the simplest five-dimensional (5D) RS-II brane-world cosmology. In this paper, we consider the constraints on both the meanings of dark radiation-based upon the newest results for light-element nuclear reaction rates, observed light-element abundances and the power spectrum of the Cosmic Microwave Background (CMB). Adding dark radiation during big bang nucleosynthesis (BBN) alters the Friedmann expansion rate causing the nuclear reactions to freeze out at a different temperature. This changes the final light element abundances at the end of BBN. Its influence on the CMB is to change the effective expansion rate at the surface of the last scattering. We find that the BBN constraint reduces the allowed range for both types of dark radiation at 10Mev to between $-12.1\%$ and $+6.2\%$ of the total background energy density at 10Mev. Combining this result with fits to the CMB power spectrum, produces different results for particle versus brane-world dark radiation. In the brane-world, the range decreases from $+6.2\%$ to $-6.0\%$. Thus, we find that the ratio of dark radiation to the background total relativistic mass energy density ${\rho }_{\mathrm{\text{DR}}}/\rho$ is consistent with zero although there remains a very slight preference for a positive (rather than negative) contribution.

Big Bang Nucleosynthesis (BBN) explores the first few minutes of nuclei formation during the Big Bang. We present updated 2$\sigma$ for the abundances of the four primary light nuclides — D, ³He, ⁴He, and ⁷Li — in BBN. A modified standard BBN code was used in a Monte Carlo analysis of the nucleosynthesis uncertainties as a function of the baryon-to-photon ratio. Reaction rates were updated to those of NACRE, REACLIB, and $R$-Matrix calculations. The results were then used to derive a new constraint on the effective number of neutrinos.