The Study And Calculation Of BBN Dynamic Equations

Big Bang Nucleosynthesis is one of the pillars of the cosmological model, and it is not only a window of learning the mystery of early universe but also represents one of the most powerful tools to test fundamental physics. Presently, this aspect is even more relevant than in the past. In this paper, the set of dynamic equations ruling primordial nucleosynthesis in standard BBN model have been investigated, and the demanding initial quantities in numerical calculation are presented in detail, including universal thermodynamic quantities, initial values of nuclei and reaction rates etc. The key of nucleosynthesis calculation is to choose effective numerical methods for solving the nuclear reaction network equations. Because of the particularity of astrophysical environment, the nuclear reaction network is extraordinary stiff and the stiffness ratio exceeding 1015 is not uncommon. It brings us much trouble for numerical calculations of nucleosynthesis, and the efficient numerical solution is presented. We update the data base of reaction rates and also perform network calculation with the newest rates. Next we investigate the role of the 8Li(n,γ)9Li (α,n)12B (β)12C sequence in the synthesis of CNO by carrying out the nucleosynthesis simulations with the new experimental 8Li(n,γ)9Li rate measured by experimental astrophysics group from CIAE. Two runs were devised:one was made with the chain turned off; and another was made with the chain. The calculation results show that the abundance of 12C is increased for an order of magnitude after addition of the reaction chain 8Li(n,γ)9Li (α,n)12B (β)12C which was neglected in former research. To investigate how the sequence 8Li(n,γ)9Li (α,n)12B (β)12C play role in the synthesis of CNO, we also perform the reaction fluxes calculation. By analyzing the synthesis of CNO we find that the newly added reaction opens effective main channel from light to CNO elements in standard BBN. Although the absolute yields of CNO are still small, this may be relevant to study the physics of stars formed from the collapse of the very first structure in the universe, as it is strongly dependent from the chemical composition of the cloud.