Astronomy and Astrophysics – Astronomy
Scientific paper
Apr 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003aps..apr.c3004n&link_type=abstract
American Physical Society, April Meeting, 2003, April 5-8, 2003 Philadelphia, Pennsylvania, MEETING ID: APR03, abstract #C3.004
Astronomy and Astrophysics
Astronomy
Scientific paper
The primordial abundances of the elements are our only direct probe of conditions when the universe was 1 second to 10 minutes old and temperatures were greater than 10^8 K. During this time, the ratio of neutrons to protons froze out of thermal equilibrium, subsequent reactions assembled the nucleons into nuclei up to mass 7, and finally all nuclear processes froze out. Motivated by recent claims that the fine structure constant α varies with time, I will discuss the consequences that result if α at the time of primordial nucleosynthesis was different from its present value. The dominant sources of α dependence for the primordial deuterium and lithium aundances are the Coulomb barrier that impedes charged-particle reactions and the coupling of nuclear currents to the emitted photon in capture reactions. The low charge numbers involved in big-bang nucleosynthesis require that the Coulomb barrier be treated carefully. I will show that changes in the nuclear masses due to electromagnetic interactions between nucleons have very little effect on nucleosynthesis. For ^4He and for Li at very low values of the universal mean baryon density, the abundances depend strongly on the nucleon mass splitting. Nucleosynthesis calculations are therefore limited by our knowledge of the size of the electromagnetic contribution to the splitting. I will show the results of nucleosynthesis calculations for the varying-α scenario and combine them with astronomical data to obtain constraints on combinations of α and the universal baryon density. I will further demonstrate the importance of the electromagnetic contribution to the mass splitting for these constraints.
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