Primordial deuterium abundance from calculations of $p(n,\gamma )$ and $d(p,\gamma )$ reactions within potential-model approach

The $p(n,\gamma )$ and $d(p,\gamma )$ reactions are key nuclear inputs for Big Bang nucleosynthesis. In this work, both reactions are analyzed within a consistent two-body potential framework based on the Malfliet-Tjon interaction, including contributions from both $E1$ and $M1$ transitions. A single scaling factor $\lambda$ controlling the low-energy scattering dynamics is constrained by the $p(n,\gamma )$ and propagated consistently to the $d(p,\gamma )$. The obtained abundance, $\mathrm{D}\mathrm{/}\mathrm{H}=2.479_{-0.177}^{+0.350}\times {10}^{-5}$, is in good agreement with values inferred from metal-poor damped Lyman-$\alpha$ systems. The modest variations of $\lambda$ lead to a significant change in the predicted $\mathrm{D}\mathrm{/}\mathrm{H}$ ratio and light-element abundances.