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$θ$-dependence of light nuclei and nucleosynthesis

We investigate the impact of the QCD vacuum at nonzero $θ$ on the properties of light nuclei, Big Bang nucleosynthesis, and stellar nucleosynthesis. Our analysis starts with a calculation of the $θ$-dependence of the neutron-proton mass difference and neutron decay using chiral perturbation theory. We then discuss the $θ$-dependence of the nucleon-nucleon interaction using a one-boson-exchange model and compute the properties of the two-nucleon system. Using the universal properties of four-component fermions at large scattering length, we then deduce the binding energies of the three-nucleon and four-nucleon systems. Based on these results, we discuss the implications for primordial abundances of light nuclei, the production of nuclei in stellar environments, and implications for an anthropic view of the universe.