Speaker
Description
Big Bang Nucleosynthesis (BBN) accounts for the cosmic origin of the lightest elements, and deuterium (D/H) plays a key role in probing the physics of the early universe. The simplicity of BBN theory allows for few-percent-level precision of D/H prediction, which is not normally possible in nuclear astrophysics. Under such precision, the comparison between predicted and observed primordial D/H not only provides a crucial test of the standard cosmology but also hints at new physics. The push to further improve this precision brings its own challenges and rewards: sharpening the power of BBN constraints on new physics.
The nuclear uncertainties of deuterium destruction reactions now block our way to a better D/H prediction. The reactions $d(p,\gamma)^3$He, $d(d,n)^3$He, and $d(d,p)t$ are known to dominate the D/H theory error budget. Recent cross section measurements from LUNA significantly reduced the uncertainty of $d(p,\gamma)^3$He, and the state-of-the-art D/H theory error is $\sim 3 \%$. However, this excellent theory uncertainty still falls behind the observed counterpart; precision measurements of the primordial D/H from high redshift quasar absorption systems in the past several years have contributed to an impressive $\sim 1 \%$ error. The future improvement of D/H prediction relies on new precision measurements of $d(d,n)^3$He and $d(d,p)t$ at BBN energies. Moreover, ab initio theory cross section for $d(p,\gamma)^3$He mismatches the precise LUNA data while agreeing with other datasets outside the BBN range. Additional theory study for $d(p,\gamma)^3$He cross section is also needed to understand such a puzzling discrepancy.
