Influence of the variation of fundamental constants on the primordial nucleosynthesis

REVIEW JOURNAL

TITLE             : Influence of the variation of fundamental constants

on the primordial nucleosynthesis

WRITER         : Alain Coc , Pierre Descouvemont, Jean-Philippe Uzan3 and Elisabeth Vangioni

A.    The background and research purposes

These constraints are derived from a wide variety of physical systems and span a large time interval back to Big Bang Nucleosynthesis (BBN). Using inputs from WMAP for the baryon density , BBN yields excellent agreement between the theoretical predictions and astrophysical determinations for the abundances of D and He despite the discrepancy between theoretical prediction of 7Li and its determined abundance in halo stars. The effects of the variation of fundamental constants on BBN predictions is difficult to model. However, one can proceed in a two step approach: first by determining the dependencies of the light element abundances on the nuclear parameters and then by relating those parameters to the fundamental constants, following our earlier work.

B.     Method

·         The triple–alpha

The triple-alpha reaction is a two step process in which, first, two alpha–particles fuse into the Be ground state, so that an equilibrium (2a $8Be) is achieved. The second step is another alpha capture to the Hoyle state in. In our cluster approximation the wave functions of the Be and C nuclei are approximated by two and three-cluster wave functions involving the alpha particle, considered as a cluster of 4 nucleons. It allows the calculation of the variation of the 8Be ground state and 12C Hoyle state w.r.t. The results of research and discussions

·         The He(d,p) He and H(d,n) He reactions

The He(d,p) He and  H(d,n) He reactions proceeds through the Li and  He compound nuclei and their rates are dominated by contributions of  + analog resonances. The corresponding levels are well approximated by cluster structures (Hed or td), so that we can use the same microscopic model as for the He(aa,g )12C reaction. However, unlike in the case of  Be, the He and 5Li nuclei are unbound by _1 MeV and the resonances are broad. Therefore the issue of producing A=5 bound states, or even a two step process, like the triple–alpha reaction is irrelevant.

C.     Conclusion

Through our detailed modeling of the cross-sections we have shown that, although the variation of the nucleon-nucleon potential can greatly affect the triple–a process, its effect on BBN and the production of heavier elements such as CNO is typically 6 orders of magnitude smaller than standard model abundances. Even when including the possibility that 8Be can be bound, at the temperatures, densities and timescales associated with BBN, the changes in the 4He(aa,g )12C and 8Be(a,g )12C reaction rates are not sufficient.