Effect of quark mass variation on big bang nucleosynthesis

We calculate the effect of variation in the light-current quark mass, m(q), on standard big bang nucleosynthesis. A change in m(q) during the era of nucleosynthesis affects nuclear reaction rates, and hence primordial abundances, via changes in the binding energies of light nuclei. It is found that a relative variation of delta m(q)/m(q) = 0.016 +/- 0.005 provides better agreement between observed primordial abundances and those predicted by theory. This is largely due to resolution of the existing discrepancies for Li-7. However this method ignores possible changes in the position of resonances in nuclear reactions. The predicted Li-7 abundance has a strong dependence on the cross-section of the resonant reactions 3He(d. p) 4He and t(d. n) He-4. We show that changes in m(q) at the time of BBN could shift the position of these resonances away from the Gamow window and lead to an increased production of Li-7, exacerbating the lithium problem. (C) 2009 Elsevier B.V. All rights reserved.