Abstract
We calculate the effect of variation in the light-current quark mass, mq, on standard big bang nucleosynthesis. A change in mq 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 δmq/mq=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 7Li. However this method ignores possible changes in the position of resonances in nuclear reactions. The predicted 7Li abundance has a strong dependence on the cross-section of the resonant reactions He3(d,p)He4 and t(d,n)He4. We show that changes in mq at the time of BBN could shift the position of these resonances away from the Gamow window and lead to an increased production of 7Li, exacerbating the lithium problem.
Highlights
Measurements of the primordial baryon-to-photon ratio η from the cosmic microwave background from WMAP [1], coupled with precise measurements of the neutron half-life [2], have made big bang nucleosynthesis (BBN) an essentially parameter-free theory [2, 3, 4]
While the “lithium problem” has been known for some time, it has been exacerbated by recent measurements of the 3He(α, γ)7Be reaction [5]
Standard BBN theory with η provided by WMAP 5 overproduces 7Li by a factor of 2.4 – 4.3 [4]
Summary
Measurements of the primordial baryon-to-photon ratio η from the cosmic microwave background from WMAP [1], coupled with precise measurements of the neutron half-life [2], have made big bang nucleosynthesis (BBN) an essentially parameter-free theory [2, 3, 4] In this paradigm excellent agreement has been obtained between predicted and observed abundances of deuterium and 4He (see, e.g. the Particle Data Group review [2] and references therin). BBN has a high sensitivity to Bd since its value determines the temperature at which deuterium can withstand photo-disintegration and the time at which nucleosynthesis begins Their bestfit result ∆Bd/Bd = −0.019 ± 0.005 resolved -extant discrepancies between theory and observation in both 7Li and η (or alternatively, in 7Li and 4He with η fixed by WMAP). We take into account several effects that were not previously considered, most importantly the nonlinear dependence on mq and variation of resonance positions
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