Nuclear clusters with Halo Effective Field Theory

At low energies, few-body systems with large scattering length exhibit universal features (universality) that are independent of the interaction details. Some consequences are the existence of a shallow bound state and the Efimov effect1 in the twoand three-body sectors, respectively. These universal properties have a wide range of applications, from particle and nuclear to atomic and molecular physics2,3. Universality has been put on a different light in the language of effective field theory (EFT)2,4. EFT is suitable for energies with an associated Compton wavelength λ ∼ 1/Mlo that is much larger than the interaction radius R ∼ 1/Mhi, where Mlo and Mhi are respectively the characteristic low and high momentum scales. The formalism allows for corrections of O(Mlo/Mhi), obtained in a systematic and model-independent way. For nuclear systems with A ≤ 4, it provides a convincing explanation for some few-nucleon correlations, like the Phillips5,6 and Tjon7 lines, as well as reliable error estimates for some astrophysical reactions like8 n+p → d+γ. Technical and numerical complications arise for nuclei with A > 4. There are, however, interesting situations of halos and weakly bound nuclear clusters, where large simplifications can be achieved. The typical momentum Mhi required to excite the core/clusters is much larger than the momentum Mlo that binds the clusters altogether. The degrees of freedom then become the clusters themselves9,10,11,12, usually stable nuclei like alpha particles and nucleons. In the following I present EFT studies for alpha-alpha (αα) and nucleon-alpha (Nα) interactions, which are