Abstract
We investigate the impact of the QCD vacuum at nonzero $\theta$ on the properties of light nuclei, Big Bang nucleosynthesis, and stellar nucleosynthesis. Our analysis starts with a calculation of the $\theta$-dependence of the neutron-proton mass difference and neutron decay using chiral perturbation theory. We then discuss the $\theta$-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.
Highlights
One of the most outstanding questions in physics pertains to the values of the fundamental parameters in the Standard model
The detailed study in [31], found that while some 8Be is produced in Big Bang Nucleosynthesis (BBN), no enhancement of carbon occurs as the temperature and density in the BBN environment is substantially below that in stars and the production rates are inefficient
The production of 12C in stars requires a triple fine tuning: (i) the decay lifetime of 8Be, is relatively long, and is of order 10−16 s, which is four orders of magnitude longer than the scattering time for two α particles, (ii) there must exist an excited state of carbon which lies just above the energy of 8Be + α and (iii) the energy level of 16O which sits at 7.1197 MeV must be nonresonant and below the energy of 12C + α, at 7.1616 MeV, so that most of the produced carbon is not destroyed by further stellar processing
Summary
One of the most outstanding questions in physics pertains to the values of the fundamental parameters in the Standard model. Values will permit a Universe which supports our form of life, which can carry out such measurements This is often referred to as the anthropic principle. In the present paper we revisit this issue While it is certainly true (and will be made clear below) that θ ∼ 10−9 or even θ ∼ 10−5 will not change life in our world, it seems reasonable to reconsider constraints imposed on θ from observations other than the neutron electric dipole moment (nEDM) as well as the anthropic perspective. We will only vary θ fixing all other parameters to their observed values At this point, it is worth noting that the most often discussed physical effect of θ on an observable, the nEDM arising from strong CP-violation, does not impose strong anthropic constraints on θ. The Appendix contains a derivation of the neutron-proton mass difference with varying θ
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